Answer:
-13
Step-by-step explanation:
If Diamond was using addition, then the only number that can be added to 8 in order to get -5 would be -13. This is because 13 is 5 more than 8. Therefore, a negative 13 (-13) added to 8 would mean that you would have to move to the left of the number line 13 places which would cause you to pass 0 by a total of 5 spaces to the left, leaving you at -5