15.
-9
9
9 + 9 + 9 + 9 + 9 + 9 + 6 + 6 + 6 + 6 + 2 + 2 + 23 + 3 + 3 + 4 + 4 + 4 = 123
9 + 6 + 9 + 6 + 9 + 8 + 5 + 2 + 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 = 99
It is: 18+6+6+6+6+9 = 51
9 + 9 + 9 + 1 + 6 + 5 = 39
(6 x 9) + 6 + 9 = 69
6+6+6+6+6+6+6+6+6 =54 This can also be written as 6*9. That is because 6 is added 9 times.
Commutativity.
6 + 9 + 10.82 = 25.82
5 + 6 + 9 = 20
Use BODMAS/BIDMAS/PEDMAS: 9 + 6(22 + 4) = 9 + 6(26) = 9 + 6 × 26 = 9 + 156 = 165