Rita is 12 years old and her father is 39 years old. In how many years will Rita be twice as young as her father?

2(12 + n )= (39 + n) (1)

24 + 2n = 39 +n

n = 39 -24 = 15

After 15 years Rita 's age = 12 + 15 = 27, father age = 39 +15 = 54

54 = 2 ( 27).

Notice that whole word problem was put into one algebraic statement of equation (1).