Forces P, Q and R act on a particle at O in the plane of the coordinate axes 0x, 0y. Force P acts along 0x, Q acts along 0y, and R acts at an angle $\displaystyle theta$ with 0x, in the first quadrant. Calculate the magnitude of the resultant force and the angle it makes with 0x when:

P=3N

Q=4N

R=5N

$\displaystyle theta$= 60 degrees

I worked out the resultant force by resolving 'R' into horizontal and vertical forces, but you cant work out the angle it makes with 0x by doing this. I was hoping someone with more trig knowledge could help out.