Superman needs Physics Power!

Imagine that you are superman flying back to Earth, but unexpectedly you lost your power momentarily and soon crash landed onto a NASA airspace station situated on the moon. However, you needed to go back home to save the Earth from the sinister villains in just 3 days before their planned attack. The NASA scientists thus decided to help him. Issac Newton especially, designed a device known as the Universal Projection Pad , this gadget simply adjusts to the environment and calculates the minimum projection velocity required for Superman to go back to Earth from a particular planet. Superman contemplated and wanted to find out the time taken to do so, find that time taken and save the world. Round your answer to $2s.f.$ in seconds and in standard form. Present from Issac Newton ; Physicists can be heroes too

Details :

1. Assume that the journey is vacuum, which is of course, space and that the velocity projected does not change during the journey as no external forces are included.

2. Assume that $G$ , gravitational constant is $6.67\times 10^{ -11 }{ m }^{ 3 }{ kg }^{ -1 }{ s }^{ -2 }$

3. Radius of the Moon: $1.7\times 10^{ 6 }{ m }$

4. Mass of the moon: $7.35\times 10^{ 22 }kg$

5. The journey is about $384,400km$