Mary is baking a cake. The recipe calls for w cups of sugar and x cups of flour. She already put in 2 cups of flour. How many more cups of flour than cups of sugar does she need to add now?
y = 2

x - y = 9 - 2 = 7

w - y = 6 - 2 = 4

Therefore, she needs to add 4 more cups of flour than sugar.