Okay, I'm going to assume that the part you're confused about is the part about how to use the number line to get the answer since the answer is given to you (it's -3).
So what you want to do is plot a point on -7. Since the line ends at -5, extend the line by drawing 2 vertical lines about to represent -6 and -7 (if you're reading it from left to right the -7 would come before -6 because it is a smaller value). Then you would want to hop 4 lines to the right, starting on -7. You would land on -3 which is the answer.
