Correct Answer - Option 3 : 30 years
Let age of smaller sister = x years
Age of elder sister = 24 years
Mother's age at the time of birth of younger sister = 30 years
Father's age at the time of birth of younger sister = 34 years
According to ques;
Sister age Difference = Mother and father age Difference
24 - x = 4
x = 20 years
Father's age at the north of elder sister = 34 - 4 = 30 years
Hence, "30" is the correct answer.