1 + 4 = 5

5 + 2 + 5 = 12

12 + 3 + 6 = 21

21 + 8 + 11 = 40

The answer is 40.

 

The second solution find on second page

Use this formula: a + b = a + a(b).

1 + (4 × 1) = 5

2 + (5 × 2) = 12

3 + (6 × 3) = 21

8 + (8 × 11) = 96

The answer is :96.
Source

1 2