For S if the ratio is 2:7 and you use 20 drops of red paint you multiply 2 by 10 which is 20 so you also multiply 7 by ten to get 70 (So the answer for S is 70 drops) and for L you multiply 2 by 20 to get 40 so you multiply 7 by 20 and you get 140 (The answer for L is 140 drops) For T you multiply 2 by 1.5 to get 3 so you multiply 7 by 1.5 which is 10.5 ( so the answer for T is 10.5 drops)