Gravitation

A rocket is fired vertically with a speed of $4 \mathrm{~km} / \mathrm{s}$ from the earth's surface. How far from the earth does the rocket go before returning to the earth?

(Take, radius of earth $=6.4 \times 10^6 \mathrm{~m}$ and $g=10 \mathrm{~m} / \mathrm{s}^2$ )