Respuesta :

TSO
Nice question! The rule is:

a + b = a(b + 1)

So...

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

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

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

8 + 12 = 8(12 + 1) = 8(13) = 104

The answer is 104.