Speed an asteroid

Hi
This problem makes me confuse, would you help me abut that:

A NASA satellite has just observed an asteroid that is on a collision course with the Earth. The asteroid has an estimated mass, based on its size, of 5 X 10^9 Kg. it is approaching the Earth on a head-on course with a velocity of 600 m/s relative to the Earth and is now 5.0 x 10^6 km away. The average force of air resistance is 3.7 x 10^11 N as the asteroid moves 300 km through the atmosphere. With what speed will it hit the Earth's surface (assume the mass of the asteroid stays constant as it moves through the atmosphere)?

Thank you