Wyatt uses 3.15 cups of flour in a recipe that makes 9 shortcakes. cora uses 2.4 cups of flour in a recipe that makes 8 shortcakes. how much more flower per shortcake is needed for cora’s recipe?

For Wyatt's recipe the rate is:
 r1 = 3.15 / 9
 r1 = 0.35
 For Cora's recipe the rate is:
 r2 = 2.4 / 8
 r2 = 0.3
 The difference between both recipes is:
 r1-r2 = 0.35 - 0.3 = 0.05
 
 0.05 cups of flour per shortcake less is needed for Cora's recipe