Step-by-step explanation:
There is a pattern involved here.
1+4 = 5
2nd step :2+5 = 7
Add 5 and 7 i.e 12
3rd step: 6+3 = 9
Add 9 and 12 i.e 21
4th step :8+11 = 19
Add 21 and 19 i.e 40
1+4=5
2+5= 12
3+6= 21
8+11=40
