The area and the amount of gravel are illustrations of proportions.
7 lb will cover an area of 1 square foot, while 315 lb will cover an area of 45 square feet.
The given parameters are:

The number of pound for an area of <em>1 square foot </em>is calculated as follows:

So, we have:


Cross multiply

Divide both sides by 36

The area to be covered with 315lb gravel is calculated as follows:

So, we have:


Cross multiply


Divide both sides by 252

Hence, 7 lb will cover an area of 1 square foot, while 315 lb will cover an area of 45 square feet.
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