I think she may just want him to write 3n-5, instead of 3(n-1)-2.
Which - of course - are mathematically the same. This is so painful to see. Was it like this when we were kids and we just didn't realize it?
Well... my math teachers wanted things written in simplest form, so they would have wanted this equation written with n instead of n-1. It may seem silly at this level of math, but it gets to be helpful as you move into more complicated equations.
Did the teacher take points off for it or just point out that it wasn't in simplest form? And did the instructions ask for it in simplest form? (you don't have to actually answer those questions - just pointing out that this example doesn't sound like an issue that I'd lose any sleep over).
Best wishes,
polarbear
