Question 824988
18/3 is 6, so 6 cupcakes can fit along the short side of each box. 31/2 is 15.5, so 15 cupcakes will fit along the long side of each box since you probably can't cut them in half. 6 * 15 = 90 cupcakes per box.
2 boxes can hold 180 cupcakes, 3 boxes can hold 270 cupcakes, 4 boxes can hold 360 cupcakes, 5 boxes can hold 450 cupcakes.
You will need 5 boxes to hold 420 cupcakes.