Gary lost 17 pounds while on a diet, but gained 8 pounds back. which number is the additive inverse of the change in gary's weight?

If Gary lost 17 pounds and gained 8 pound back, then we have
 -17 pounds + 8 pounds = -9 pounds.
 Therefore the additive inverse of the change in Gary's weight is 9 pounds.
 That is, Gary lost 9 pounds of weight.