Hard? I found the hard one fairly easy, and don’t think I accidentally spotted the solution early. For difficult, I would expect at least one division, as in (ax+b)/(c-d)

But yes, I factored the result in my head. I would have done the same with (result ± any of the other numbers), if necessary.

Also, for the simple one, I immediately recognized 243 as a power of 3, so maybe, I’m not in the target group ;-)