Answer: The logic followed by the equations are as follows

1 + 4 = 1 x (4 +1) = 1 x 5 = 5

2 + 5 = 2 x (5 + 1) = 2 x 6 = 12

3 + 6 = 3 x (6 + 1) = 3 x 7 = 21

Therefore we can find the missing number as;

8 + 11 = 8 x (11 + 1) = 8 x 12 = 96