Please help with this wave question !?

Tuning the piano (f = 523.3 Hz), the pianist heard a beat of 3 Hz. Then he tightens the string and he heard a beat of 2 Hz. So what is percentage of the tension in the string if assume linear mass density is 0.5g/m .

So here where I stuck I refer to the formula v = √(T/μ) <<< where T is tension So how ? please explain. Thank you very much for your time.