Question 778380
son's age : x
father's age : 4x

in 10 years
son's age: x + 10
father's age: 4x + 10

4x + 10 = 2 (x + 10)
4x + 10 = 2x + 20
2x = 10
x= 5

son's age: 5
father's age: 4(5) = 20