Lets change the equation.
3 -(3*6) +2 Multiply 3*6 first and get 18
3 -18+2 - Same as 3-(18)+2
-15 +2 3 -18 is the same as doing 18 -3, but with the negative
Do the same to -15 +2
Answer is -13
The sum to 6+7 is 13 and the answer to 8+4 is 12 and the sum to 2+9 is 11