If you have 5 boards, and one person take one from you, how many do you have left

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?

Jimmy can run 3.5 miles in 20 minutes. how far can ne run in one hour and ten minutes?

Either enter an exact answer in terms of \piπ or use 3.143.14 for \piπ and enter your answer as a decimal.