A fruit juice recipe calls for 5 parts orange juice and 6 parts pineapple juice. Which proportion can be used to find the amount of orange juice, j, that is needed to add to 21 L of pineapple juice?
30 over 21 equals j over 100
6 over 5 equals j over 21
6 over j equals 5 over 21
5 over 6 equals j over 21
