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.
the answer is 9 because inverse means oppisite and since its a additive inverse is will change to a positive and -17 - 8 = -9 since its a additive inverse it will change to a positive which will = 9
