Question 44787
They gave you the diameter of the circle in the question.  The diameter of a circle is equivalent to twice its radius.  That is:  {{{d=2r}}}.  We know from the question that the diameter of this crop circle is 25 meters.  So let's plug that in to the formula and that'll give us the radius of the circle.  

{{{25=2r}}}
{{{r=25/2}}}
{{{r=12.5}}}

Now that we know the radius, which is 12.5 meters.  Let's plug that into the formula for the area of the circle to get our answer:

{{{A=pi*(12.5)^2}}}
{{{A=490.87}}}

You also could compute {{{12.5^2}}} and leave {{{pi}}} alone.  In that case,

{{{A=156.25pi}}}