Question

A store display will have 6 rows, with 12 containers in each row.

If 39 containers has been set up so far, explain how to find the
number of containers that still need to be set up. Then solve the
problem

Answer 1

A total of 72 containers need to be set up. If 39 are already placed then there are 33 left. You multiple the number of rows by the number of containers per row to find your total and subtract what has already been done.