Suppose that three Civilian Conservation Corps members, Richard, Nancy, and John, had to build a rock wall. They had to move 21 boulders across a field. Seven of the boulders were
large, weighing 25 pounds each. Seven of the boulders were medium-sized, weighing 20
pounds each. Seven of the boulders were small, weighing 15 pounds each. Each worker had
a wheelbarrow. They agreed to share the task equally. Each person carried the same number
of boulders and the same number of pounds. How did they manage to do this?