What should come in place of the question mark (?) in the following? Three figures with numbers: Figure 1 has 16, 21, 15, 10 surrounding 36; Figure 2 has 7, 10, 13, 10 surrounding 16; Figure 3 has 15, ?, 21, 14 surrounding 64

Explanation

As 21 – 16 = 5 and (5 + 1)2 = 62 = 36 or 15 – 10 = 5 and (5 + 1)2 = 62 = 36 (middle number) and 10 – 7 = 3 and (3 + 1)2 = 42 = 16 or 13 – 10 = 3 and (3 + 1)2 = 42 = 16 (middle number) Similarly 21 – 14 = 7 and (7 + 1)2 = 82 = 64 (middle number) ∴ ? – 15 = 7 ? = 7 + 15 = 22