Poor/poverty is defined by earning less than $2/day, taking into consideration purchasing power parity. You do not know what poverty is till you cross that line. Things start to get really ugly!
The urban poor are in a far more desperate position than the rural poor, regardless of their country's development. Compare Depression-era Kansans to the inner-city poor of today and you'll see a large disparity in just about every metric. The one that jumps out at me the most would be nutrition. It's a lot easier to eat well with no money on a farm than it is with no money surrounded by convenience stores and Taco Bells.
Which is irrelevant since the $2 a day figure is adjusted for purchasing power parity.
In the U.S. poverty is defined as earning less than $23,050 for a family of 4 or $14,657 for a family of 2 (in 2011). My average yearly take back then was around $13k. My best year was $16k. The difference materially for us was that I paid more taxes at $16k than $13k, and we ate something other than Ramen and Taco Bell once a week.
Despite being eligible for welfare, we chose never to take it since we were both healthy and could (theoretically) work and if we watched out finances, make ends meet. It was hard, but we did it until I got sick.
Even in 1990, $14,000 was 'only' 3700 hours of minimum wage work, that's not 2 full time jobs, never mind 100 hours a week (I would think it fair to include school time as work, but it would also be fair to mention it). If this all happened before then, the 2011 poverty line isn't a very interesting point of reference.
For money: let's start with your $14k/yr. Now deduct witholdings, then $900 a month for rent. For fun I checked, in the area I lived in back then, there are 0 apartments under $1200 a month today. Housing is expensive.
So say 20% disappears for witholdings ($2800) = $11,200/yr less $10,800 for rent = $400 to do everything else on for the year. Or about $33 a month for food, fuel, clothes, transport, etc. It's about a dollar a day. Good luck. Hope you don't also have car payments.
For time that's also easy. There's about average 30 days to a month or 720 hours. That's your time "budget". You can never have more or less than that.
Minus a full-time job, 40 hours = 548.
Minus 2-4 hours a day during work weeks taking either the car or the bus depending if you want time or money. So around another 40-80 hours a month disappears (you can't get to work in zero time). leaves you with 468-508 hours left
3-4 hours a day eating..~120 hours a month. 348-388 hours left.
You gotta sleep. Lets say you're generous and give yourself 7 whole hours a night. 228-268 left.
Now if you're going to school like I was, you're in class 12-16 hours a week with about 3x that much out of class work. So 124.3=51.6 leaves you with ~177-216.
1234.3~155 hours leaves you with 22-61 hours.
Let's say you go to school 3 days a week. Take out 1-2 hours (car or bus) for transport per school day or about 13-25.8 hours per month leaves you with...well pretty much not enough hours to do anything else.
So you stretch, you knock off an hour or two a day for sleep, leaving you chronically sleep deprived. If you decide that you can't afford the time, you drive everywhere, which drives up your fuel costs. But it leaves you enough time during the week for a second full-time job and maybe some extra work on the weekends when you can get it. But you're so tired you can't focus on what's going to get you out of this mess, your school work.
So you work two part-time jobs so you can keep your grades and studies up. But you're still sleep deprived. If you don't get work one weekend, you might sleep through the entire weekend in one stretch. A side benefit is that you didn't have to pay for food while you were sleeping (a strategy you'll see among many of the homeless population in most urban areas).
Or you work one full and one part-time job and go to school less than full-time, but you lose one of your grants and can't afford school that way anyway.
It's a very* hard multi-variable equation that you have to balance, minute by minute, and hour by hour.
Heaven forbid you have a bad day and need a couple extra hours, or want to spend a couple hours unwinding in front of the TV. You can't get more time.
There were many times that I looked into getting illegal modafinil because I heard you could go without sleep for a couple days at a time. It would "buy back" 20-30% of my monthly hour budget letting me work more...or giving me time to study.
Trying to understanding being poor without understanding time budgeting will give you a very incomplete picture. There's a reason so very few people go to school and work at the same time even though a naive look at their hours makes it look trivially possible.
In 1990, with $3.80 minimum wage, that would have been 7904. I think your calculations are wrong.
"'only' 3700 hours" probably wasn't the best way to phrase it, but I was trying to establish that it would have been possible to earn $14,000 at low wage jobs in 1990, and it seems like it would have been.