We have to find the area when we have the circumference which is 31.4ft. state the problem with complete sentences.

The formula for the circumference of a circle is π x diameter
Since we already know the circumference, we divide that by π to get the diameter:

circumference = π x diameter             
so 
circumference / π = diameter 

Now lets do this:

31.4 / π = 9.9949...  (this is the diameter)


The formula for the area of a circle is π r²

To get the radius, we just halve the diameter:
9.9949.. / 2 = 4.99746...  

Now that we know the radius we can use the formula:

 π x r²
= π x 4.99746²
= 78.46ft²

So the area is:
78.46ft²