Hello!
First of all we need to find the area of this figure. First let's find the area of the small rectangle on the right.
10(16)=160
Now we add the other large rectangle.
20(25)=500
Now we add to find the total area.
500+160=660
Now we need to divide by 40 to find how many gallons of paint we will need.
660/40=16.5
Therefore, they will need 16.5 cans.
I hope this helps!