If a number is added to the numerator of 7/8, and the same number is subtracted from the denominator, the result is 2, find the number?
7/8 8/7 9/6 10/5=2
Sometimes doing it is good.
If you want to get complicated
(7+x)/(8-x) = 2
x=3 which gives (7+3)/(8-3) = 10/5 = 2