I know I'm always overthinking, but just doing the visual calculation, there are all numbers in order:
1 + 4 = 5
2 + 5 = 12
3 + 6 = 21
8 + 11 = ?
1, 2, 3, 4, 5, 6, … , 8, … , … , 11.
The difference between 5 & 12 is 7
The difference between 12 & 21 is 9
So basically, I’m