Derive an expression for the speed of sound based on van der Waals equation of state P

Question:

Derive an expression for the speed of sound based on van der Waals’ equation of state P = RT(v - b) - a/v2. Using this relation, determine the speed of sound in carbon dioxide at 50°C and 200 kPa, and compare your result to that obtained by assuming ideal-gas behavior. The van der Waals constants for carbon dioxide are a = 364.3 kPa • m6/kmol2 and b = 0.0427 m3/kmol.