we know that
the area of the ground covered by the tent is a circular area
then 
the area of a circle is equal to

Step 

Find the radius of the circular base
we know that
in the right triangle ABC-----> see the attached figure to better understand the problem

Solve for r

Step 

Find the area of the base
substitute the value of the radius in the formula of area


therefore
the answer is the option a
the area of the ground covered by a conical tent is equal to
