- (m+7n - 9)
When there's just a negative in front of the parentheses, always remember that it's going to be -1. The 1 is just invisible.
-1(m+7n - 9)
The first step is distributing.
Multiply every term inside the parentheses by -1.
(-1*m) + (-1*7n) + (-1*-9)
-1m - 7n + 9
So the answer is -1m - 7n + 9, or you can leave out the 1, making it -m - 7n + 9.