Have to figure out 1 before 2 and don't know were to start?

Question

1)The tension in the above string is 84.0 N. Calculate the mass of a 3 m long piece of the steel string.
2)Find the wavelength of the third harmonic of the guitar string described in the problem before last. Find answer in meters

Answer 1

1: You can't do this unless you have more information. Just putting tensionon a string does not change its mass.