The area of the warehouse is

Half of this area stock paint, cans and rims:

thats because the heigth of the stock room is equal to 20 ft.
On the other hand, we know that there are 2 cans in a box which volume

and a rim is inside a box with measures

Then, we need to find the ratio V_total to V_stock in order to find the number of rims in the room.
Then, V_total is the sum of 4 times the volume of one can plus the volume of 1 rim, that is,

because we need 4 cans and 1 rim in our room. This total volume is given by

which gives

The last step is convert the V_total from cubic inches to cubic feets. We can do that by means of

because 1 feet is equal to 12 inches. It yields,

Finally, we can find the ratio mentioned above:

By rounding down to the nearest interger, the ratio is 556. This means that we can stock 556 rims in the warehouse.