I have an object beind acted upon by three forces and moves with a constant velocity. One force is 60N along the x-axis, the second is 75N along a direction making a counterclockwise angle of 150° with the x-axis. What I need to find out is the direction of the third force, measured conterclockwise from the x-axis.

I am not very good at vectors and trigonometry, so if someone can give me some advice where to start and with what formula, I would very appreciate it.