Hi!
So this is an algebra question. We basically want to know what number minus 2 and 1/2 is going to equal 7 and 1/2. An easy way to check for that first number is adding those two numbers together
So we take 2 and 1/2 + 7 and 1/2 , and because they have the same denominator we can add the two numbers . 2 + 7 = 9 and then 1/2 + 1/2 = 1 so 9+ 1 = 10
10- 2 1/2 = 7 1/2