Seems like a simple problem

well heres the problem: A piano tuner detects that the "middle C" note, which should be 261.6 Hz, is too low by 12.6 Hz. If the original tension was 754 N, what must it be adjsuted to so the note plays the correct frequency?

however i have no idea where to even start?! i got these formulas but i was never given a 4th value like the density (mu) or the velocity of the note in the wire where to go!

$$v = \sqrt{\frac{T}{\mu}}$$
$$v = \lambda f = \frac{\lambda}{t}$$ where t is the period, and T is the tension in the string

as well as this one.. i think its a porportionalitly question im not sure though please help me even get started

A string is made of two materials of different mass per unit length, 2.31 g/m on the left and 3.25 g/m on the right, connected together at the center. If the wavelength of the wave on the left segment is 21.7 m, what is the wavelength on the right?

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