We are given statement " gained 20 pounds and loses 15 pounds".
Note: We take plus or positive sign for gain word and we take minus or negative sign for the loses word.
Gained 20 means +20.
Loses 15 mean -15.
Therefore, we can setup an expression as:
+20 -15.
20 is a positive number and 15 is a negative number.
Because we have opposite signs of numbers, we would subtract them.
20-15 = 5 pounds.