What is the independent variable-
number of dogs or number of total scoops of food

 -25 degrees Celsius

=========================================================

Explanation:

Draw a vertical number line. Plot -20 on it. Then move 5 units down to arrive at -25. Think of it as a thermometer where the temperature can be measured below 0 degrees, or you could think of it like floors of a building. Negative values would be basement floors.

The diagram below describes what's going on when we compute -20-5 = -25.