physics-block swinging on a string?

Can someone please explain the solution to this problem?
A 168.3 g block on a 62.3-cm-long string swings in a circle on a horizontal, frictionless table at 84 rpm. What is the speed of the block? (I got 5.4802 m/s)
What is the tension of the string? (I'm stuck on this part.)
 
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