To solve this problem, you can make a proportion:
3/900 = x/2100
In this case, the x represents the pounds that will be needed to cover 2,100 feet.
The first step is to cross multiply like this:
3 * 2100 = 900 * x
Now you can simply the equation.
6300 = 900x
Now you divide both sides by 900 to cancel it out.
7 = x
So, your answer is 7 pounds.
