Uniform Circular Motion - Finding Fc/Ft without mass

[Elatric]

Homework Statement

A boy ties a rock to a 0.95 m string and swings it in a horizontal circle directly over his head so that it completes one revolution every 0.75 s. What is the tension in the string?
So we know r and we can calculate V, but that's all I can deduce

Homework Equations

Fc=(mv^2)/r
V=(2*pi*r)/t

The Attempt at a Solution

2*pi*.95/.75= 7.9587 m/s
That's how far I got. I know the masses cancel with ma=mv^2/r but then I end up finding the acceleration. Help?

 

[rude man]

I think you need m.