The midpoint means that it is in the middle. So 3x+8=5x-1. You need to find x to really fine the amount. Could be 8x+7, but if you want to find the amount without x you need to find x.
3x+8=5x-1
3x-3x+8=5x-3x-1
8=2x-1
8+1=2x-1+1
9=2x
9/2=4.5
if x is 4.5 then all you need to do is multiply 8 by 4.5 and then add 7. You will get 43.
