Kevin is two times as old as Bob. Four years ago the sum of their ages was 10. How old is each now?

Let the age of bob be x years

Age of Kevin = 2x

Four years ago age of both would be (x-4) & (2x-4)

Equation will become

(x-4) + (2x-4) = 10

3x -8 = 10

3x = 18

X = 6

Age of bob is 6 years and age of Kevin is 2x i.e. 2*6=12 years