The other tutor doesn't understand the problem.  He doesn't
know that a cyclic quadrilateral is a quadrilateral with all
four vertices lying on a circle:





We use Brahmagupta's formula to find the area of
the cyclic quadrilateral.

 where ,

and 

a=5, b=4, c=7, and d=10

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To find the radius.

Parameshvara's formula for the radius of the circumscribed circle is



We have already calculated the denominator above as 1296, so we have




Edwin