How many cups of grape juice containing 10% fruit juice and berry punch containing 20% fruit juice must be added together to create 12 cups of punch with 18% fruit juice?

It is 2.4 cups of 10% fruit juice and berry punch and 9.6 cups of 20%fruit juice:

let x to be 10% fruit juice and berry punch and y = 20% fruit juice

. x+.2y=2.16

x+y=2.4

use substitution property or elimination property to solve the problem:

x=2.4 and y=9.6