Computer science question that also involves math, NEED HELP!!!!?

A triangle is inscribed in a circle, that is, the vertices of the triangle are on the cirference of the circle. Suppose the triangle ABC divides the cirference into lengths a,b,c inches. Design an algorithm and write A PSEUDOCODE THAT ASKS THE USER TO SPECIFY THE VALUES OR A,B,C AND THEN CALCULATES the radius of the circle. Note that if r is the radius of the circle, then 2pi(r) = a+b+c