1 + 4 = 5 2 + 5 = 12 3 + 6 = 21 8 + 11 = ?

1+4=5
You have 5.

2+5=7
Add 7 to 5 to get 12;
5+7=12

3+6=9
Add 9 to 12 to get 21;
12+9=21

8+11=19
Add 19 to 21 to get 40;
21+19=40

The answer is 40.