Answer : 4. "96"
Explanation :

Answer: D) 96 Explanation: Here in the given number puzzle, the given numbers follows a pattern that  1 + 4 = 5 => 1 x 4 + 1 = 4 + 1 = 5  2 + 5 = 12 => 2 x 5 + 2 = 10 + 2 = 12    3 + 6 = 21 => 3 x 6 + 3 = 18 + 3 = 21  Similarly,  8 + 11 = 96 => 8 x 11 + 8 = 88 + 8 = 96   Hence, the missing number in the given number puzzle is 96.