I need help please I don’t understand

Each of the walls of a room with square dimensions has been built with two pieces of sheetrock, a smaller one and a larger one. the length of all the smaller ones is the same and is stored in the variable small. similarly, the length of all the larger ones is the same and is stored in the variable large. write a single expression whose value is the total area of this room. do not use any method invocations.

What is the missing step in this proof ?

What is the unit rate of, 75% high fiber chimp food to 25% high protein chimp food.