A cannonball was shot out of a tower.

The cannonball left the window at a horizontal speed of 20 metres per second, and the window was at a height of 45 metres, and the ground outside of the tower was perfectly horizontal, and the cannonball's mass was 6.2 kg. Assume gravitational acceleration of 9.8 metres per second squared.

How much horizontal distance will the cannonball travel from the tower before hitting the ground?

This problem has been bugging me for a while. There are no additional forces. Could someone explain how to get the answer please?

Thanks,

Simon