3 years ago, a father's age was 24 years more than twice his son's age. After how many years from now will his age be twice his son's age?

Correct option is D

Given:

3 years ago, father's age = 2 × son's age + 24

After how many years (x) will father’s age = 2 × son’s age?

Solution:

Let present age of son = S years

Let present age of father = F years

Condition 3 years ago:

F - 3 = 2(S - 3) + 24

F - 3 = 2S - 6 + 24

F - 3 = 2S + 18

F = 2S + 21

Future condition:

F + x = 2(S + x)

Substitute (F = 2S + 21):

2S + 21 + x = 2S + 2x

21 + x = 2x

x = 21 years ​