Proton and carbon collision

[envscigrl]

A proton of mass m undergoes a head-on elastic collision with a stationary carbon nucleus of mass 12×m. The initial velocity of the proton is 790 m/s in the positive x direction. Find the velocity of the center of mass of the system.

I am really confused as to how to find the 'velocity of the center of mass'. I thought using the equation Mv = mv1 + mv2 would work but nope it surely didnt. I am not sure if I am missing an equation or what but I cant seem to figure it out.
Thanks for your help and time!

[ehild]

A proton of mass m undergoes a head-on elastic collision with a stationary carbon nucleus of mass 12×m. The initial velocity of the proton is 790 m/s in the positive x direction. Find the velocity of the center of mass of the system.

I am really confused as to how to find the 'velocity of the center of mass'. I thought using the equation Mv = mv1 + mv2 would work but nope it surely didnt. I am not sure if I am missing an equation or what but I cant seem to figure it out.
Thanks for your help and time!

I do not see any problem with that equation.
V = (m1v1+m2v2)/(m1+m2) = (790*m+0*12m)/(13m) = 60.8 m/s in the positive x direction is really the velocity of the center of mass.

ehild