The units of the rate constant are very simple to find. You must first find the rate law of the reaction. Then, you must set up the rate equal to that reaction's rate law. Since the reaction rate is always molarity/second. Then you just plug in the M for molarity for each part of the rate law. Then you simply simplify.
rate=K[W]^2[K]
M/s=K[M]^2[M]
M/(s*M^-2*M)=K
M^-2S^-1=K
rate=K[W]^2[K]
M/s=K[M]^2[M]
M/(s*M^-2*M)=K
M^-2S^-1=K
"Determining Units of a Rate Constant." YouTube. YouTube, n.d. Web. 29 May 2014.