Let 
be the number of boxes the team brings with them. Their weight combined with the boxes can't exceed the capacity of 1400. Assuming the elevator runs fine at that exact weight, you want to find the number of boxes, each of which contributes 40 pounds. This is given by the equation
Solving for, you have
So the team can bring *at most* 5 boxes at a time.
Solving for
So the team can bring *at most* 5 boxes at a time.