Consider a wave generator that produces 10 pulses per second. the speed of the waves is 3m/s, what is the wavelength?

Wave speed = (frequency) x (wavelength)

3 m/s = (10 / sec) x (wavelength)

Divide each side by (10/s) :

Wavelength = (3 m/s) / (10 / s)

Wavelength = 0.3 meter

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.