find the difference
6 - (-9) = ?
The difference between 6 and -9 is 15.
To see why, you can change the problem to addition:
6 + 9 = 15
When you subtract a negative number, it's the same as adding the opposite (positive) number. So, -(-9) becomes +9.
Then you can write the problem as:
6 + 9 = 15