Question 321958
let son's age be x
Mary's age = 3x
..
12 years later
son will be x+12
Mary will be 3x+12
..
3x+12 = 2(x+12)-1
3x+12=2x+24-1
3x-2x=24-12-1
x=11 --- son's age
Mary's age = 3*11 = 33 years