we know that
1) Wyatt uses 3.15 cups of flour in a recipe that makes 9 shortcakes
so
3.15 cups-------------> to make 9 shortcakes
x cups----------------> 1 shortcakes
x=3.15/9----> x=0.35 cup/shortcakes
2) Cora uses 2.4 cups of flour in a recipe that makes 8 shortcakes
so
2.4 cups-------------> to make 8 shortcakes
x cups----------------> 1 shortcakes
x=2.4/8----> x=0.30 cup/shortcakes
difference=[0.35-0.30]=0.05 cup/shortcake
Cora uses 0.05 cup of flour less per shortcake than Wyatt