Answer: 63 Juice boxes
Step-by-step explanation: So you know that 7(cartons of milk)+3(juice boxes)= 10 so you divide 210 by 10 and you get 21. 21x3 is 63 so 63 juice boxes are sold. To check the answer i did 21x7 and i got 147. 147+63=210
63 juice boxes and 147 cartons of milk are sold.