Mary is baking a cake. The recipe calls for w cups of sugar x cups of flour and y cups of salt. She already put in z cups of flour. How many more cups of flour does she need to add?
Mary is baking a cake. The recipe calls for w cups of sugar x cups of flour and y cups of salt.

So far, Mary has put in z cups of flour.

To find out how many more cups of flour she needs to add, we can subtract the z cups of flour she has already put in from the x cups of flour the recipe calls for.

x - z = cups of flour needed