[Algebraic expressions questions] 1. 11 more than a half number 2. the sum of triple z and half of x 3. 1/2 the difference of a number and 15 4. 4 less than the quotient of x and -5

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?