Solve for the empty spaces one by one. 6 times what equals 18? What is the product of 20 and 6?
Smaller steps like these make completing the whole rectangle easier.
A few of the spaces are filled in to help you get started.
One of these products is 20(40), which equals 800. Can you find at least three more like it?
If you are up for a challenge, there are eight more to find.