Solution:The pattern followed here is :Row wise pattern → (2a + 3c) = b
(13, 50, 8) → {(2 × 13) + (3 × 8)} ⇒ 26 + 24 = 50
(12, 39, 5) → {(2 × 12) + (3 × 5)} ⇒ 24 + 15 = 39
Similarly,
(15, 51 ,? ) → {(2 × 15) + (3x)} = 51 ⇒ 3x = 51 - 30 ⇒ x = 21 ÷ 3 = 7
Hence, "7" is the correct answer.