Hello!
When an equation adds a negative number (and the + and - signs are directly next to each other), the + is always turned to a minus.
In this case, the 6+(-9) would simply turn into 6-9.
Because 6 is subtracting a larger number than itself, you know that the final answer will be a negative number.
6-9= -3
The correct answer to this question is -3.
I hope this helps you!
