2.- 3/4 cups --------------------------- 12 tablespoons
x --------------------------- 13 tablespoons
x = (13 x 3/4) / 12
x = 0.8 cups
3.-
3/4 cups -------------------- 12 tablespoons
20 cups -------------------- x
x = (20 x 12) / 3/4
x = 320 tablespoons
4.-
1 cup ---------------------- 16 tablespoons