In Figure a string, tied to a sinusoidal oscillator at P and running over a support at

Question:

In Figure a string, tied to a sinusoidal oscillator at P and running over a support at Q, is stretched by a block of mass m. Separation L = 1.20 m, linear density ? = 1.6 g/m, and the oscillator frequency f = 120Hz.The amplitude of the motion at P is small enough for that point to be considered a node. A node also exists at Q.(a) What mass m allows the oscillator to set up the fourth harmonic on the string?(b) What standing wave mode, if any, can be set up if m = 1.00 kg?