What is the mass of the hanging mass (m)?

Consider what is shown below. 

A 20.00-kg mass rests on a frictionless ramp inclined at 45°.  

A string with a linear mass density of μ=0.025kg/m is attached to the 20.00-kg mass. 

The string passes over a frictionless pulley of negligible mass and is attached to a hanging mass (m). 

The system is in static equilibrium. 

A wave is induced on the string and travels up the ramp. 

(a) What is the mass of the hanging mass (m)? 

(b) At what wave speed does the wave travel up the string?