Correct Answer - Option 4 : 3 years
Given
Sum of father's age and mother's age = 51 years
Calculation
Let the age of the son is z
Father’s age = 9z and mother’s age = 8z
So, 9z + 8z = 51 years
⇒ 17z = 51 years
⇒ z = 3 years
∴ The age of the son is 3 years