I'm not doing your homework for you, but I'll tell you how to do it. 4 - (-15) Do "same, change, change," which means when you are working with subtraction, keep the first number (four) the same, change the subtraction to addition, and change the negative or positive number (in this case, -15) to the REVERSE sign. (This would be +15, but if you had a positive number to begin with, it would then be negative.) So, then do the math. 4 + 15.