If 1 o 4 = 5; 2 o 5 = 12; and 3 o 6 = 21 then what is 8 o 11 = ??

Question

If possible fill + or - for o and make this true, if not possible then provide the reasoning...

1 o 1/2 o 1/3 o 1/4 o 1/5 o 1/6 o 1/7 o 1/8 o 1/9 o 1/10 o 1/11 o 1/12 = 0

Answer 1

1 o 4 = 5; (1*4)+1=5
2 o 5 = 12; (2*5)+2=12
3 o 6 = 21 (3*6)+3=21

8 o 11 = (8*11)+8=96

Answer 2

96,
1 o 4 = 1+(1x4) = 5
2 o 5 = 2+(2x5) = 12
3 o 6 = 3+(3x6) = 21
Similarly,
8 o 11 = 8+(8x11) = 96

Answer 3

It follows the logic below:
(1x4) + 1 = 5
(2x5) + 2 = 12
(3x6) + 3 = 21

Then
(8x11) + 8 = 96
The answer is 96