While skiing, sam flies down a hill and hits a jump. he has a mass of 75kg and he leaves the jump at 18 m/s what is his momentum as he leaves the jump?

First off, you need to review the formula for momentum:

                     Momentum  =  (mass) times (speed)

                                           =  (75 kg)  x  (18 m/s)

                                           =         1,350 kg-m/s  .   

There it is.  That's all there is to it.

Notice that you would have been sunk without knowing
the equation for momentum.  It's pretty important.  You
should memorize it.  You'll need it again.