Can someone explain to me how to get the answer to 63-64

Using the work energy theorem. what is the velocity of a 850kg car after starting at rest when 13,000j of work is done to it.

Two identical stars with mass m orbit around their center of mass. each orbit is circular and has radius r, so that the two stars are always on opposite sides of the circle. (a) find the gravitational force of one star on the other. (b) find the orbital speed of each star and the period of the orbit. (c) how much energy would be required to separate the two stars to infinity?

Which describes increasing the efficiency of energy resource