The equation for the area of a circle is,

But first we need to find the radius. Simply divide the diameter by 2 to get the radius.
5 ÷ 2 = 2.5
So our radius in this case is 2.5 feet.
Substitute the number,

Solve for the square,

A ≈ 19.63 ft^2
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I hope that helps you out!!
Any more questions, please feel free to ask me and I will gladly help you out!!
~Zoey