How many times can you make 36 out of those two numbers? Alone, 6x6=36 (6+6+6+6+6+6=36) and 18x2=36 (18+18=36) and then 18+6+6+6=18 because 6x3=18.
She is going to practice piano for 80 minutes. First you want to divide the number of minutes in the lesson by 5 to find how many times 5 minutes goes by in 20 minutes. Next you want to multiply your answer for that, which should be 4, by the amount she wants to practice. So you do 4 x 20, and get 80 minutes total.
4 cups of milk are needed for 8 servings.