x = number of comics Ross bought
A = 10*x = amount spent on buying those x number of comics at $10 each
B = 17*(x-1) = amount Ross gets from selling every comic book except one
B-A = 17*(x-1)-10x = 7x-17 = profit = 49
7x-17 = 49
7x = 49+17
7x = 66
x = 66/7
x = 9.42857 approximately
Because x isn't a whole number, I'm thinking that there's a typo in the problem somewhere. I would double check with your teacher.
