Write a system of equations to describe the situation below, solve using substitution, and fill in the blanks.

ying works in the shipping department of a toy factory that makes radio-controlled helicopters. small helicopters weigh 3 pounds each, and are shipped in a container that weighs 18 pounds. large ones, on the other hand, weigh 4 pounds apiece, and are shipped in a container that weighs 12 pounds. if these boxes can hold a certain number of helicopters each, all of the packed containers will have the same shipping weight. how many helicopters would fit in either container? what would the total weight be?