The answer is 5 bags.
Step 1. Find the volume (V) of the box.
Step 2. Calculate how many bags of fertilizer (x) fill the box completely.
Step 1.
The volume of the rectangle is:
V = l * w * h
1 ft = 12 in
l = 6 ft = 6 * 12 in = 72 in
w = 3 in
h = 9 in
V = 72 * 3 * 9 = 1944 in³
Step 2.
Each bag of fertilizer contains 0.225 cubic foot
1 ft = 12 in
(1 ft)³ = (12 in)³
1 ft³ = 1728 in³
0.225 ft³ = 0.225 * 1728 in³ = 388.8 in³
So, each bag of fertilizer contains 388.8 cubic inches
If 1 bag is 388.8 cubic inches, x bags will be in 1944 cubic inches
1 : 388.8 = x : 1944
x = 1 * 1944 : 388.8
x = 5 bags
