What is the inverse of the function f(x)=2x-10

Answer this question only if you know the 30 points and

If a || b and b | y, then ? a) x || y. b) x | a. c) a | y. d) a || y.

Suppose that sahil knows that 45 people with ages of 18 to 29 voted. without using a calculator, he quickly says then 135 people with ages of 30to 49 voted. is he correct? how might sohil have come up with his answer so quickly?