Physics
posted by Bobby .
A 45 kg cart is moving across a frictionless floor at 1.7 m/s. A 60 kg boy, riding in the cart, jumps off the cart so that he hits the floor moving forwards in the initial direction of the cart's motion with a velocity of 2.8 m/s. What is the velocity of the cart after the boy jumped?

initial mass = 45 + 60 = 105 kg
initial momentum = 105 * 1.7 = final momentum
so
105*1.7 = 2.8*60 + 45 v 
but how do you go from 105*1.7 = 2.8*60 + 45 v to the answer?? i'm so confused!

This is pretty basic algebra.
subtract 2.8*60 from each side. Then divide both sides by 45.