3 forces act on a moving object. 1 force has a magnitude of 80 N and is directed due north. The other has a magnitude of 60 N and is directed due west. What must be the magnitude and direction of the 3rd force, such that the object continues to move with constant velocity??

I have no clue where to start. Can someone get me started. Thanks.

Do I have to use 2d kinematic formula for this??

thanks