Correct option is D
In this question following logic is followed-
(1st + 3rd) ÷ 2 = 2nd Number
9, 20, 31→ (9 + 31) ÷ 2 = 40 ÷ 2 = 20
38, 49, 60 → (38 + 60) ÷ 2 = 98 ÷ 2 = 49
Similarly,
14, 24, 34 → (14 + 34) ÷ 2 = 48 ÷ 2 = 24
Thus, the correct answer is (d).