Assuming you mean (3 ft / 2) - 12 1/16 inches, it's about 6 inches, which is probably the accuracy you need. But it's exactly 5 15/16 inches, which is also easy to do in your head. Carpenters do it all the time, and even a doctor can.
I don't know which is better. Considering how nothing stops you from doing decimal inches or fractional meters, but people rarely do that, both ways seem fine.
But also like, we have calculators…