Find the work w1 done against gravity when the rocket rises

Question

A rocket lifts off the pad at Cape Canaveral. According to Newton's Law of Gravitation, the force of gravity on the rocket is given by

F(x) = - GMm/x²

Where M is the mass of the earth, m is the mass of the rocket, G is a universal, constant, and x is the distance (in miles) between the rocket and the center of the earth. Take the radius of the earth to be 4000 miles, so that x ≥ 4000 miles.

Find the work, w₁, done against gravity when the rocket rises 1400 miles.

Next, find the limit of the work, w₂, as the rocket rises infinitely far from the earth.