In order to solve this equation, let's write it out in number form:
-3 - x = -10
In order to isolate 'x' we need to ensure that there is only 'x' on one side. We can get rid of the -3 by adding 3 to both sides:
-3 + 3 - x = -10 +3
-x = -7
Because there are negatives on both sides, you can simply cancel them out:
x = 7
