Answer : 4. "29 yrs"
Explanation :

Answer: D) 29 yrs Explanation: Let the avg age of 7 boys be 'p' yearsLet the age of the girl be 'q' yearsFrom given data,The age of 7 boys = 7p yearsNow the new average = (p + 1) when 22 yrs is replaced by qNow the age of all 7 will become = 7(p + 1) yrsHence, 7p - 22 + q = 7(p + 1) yrs7p - 22 + q = 7p + 7q = 22 + 7 = 29 Therefore, the age of girl = q = 29 years.