mechanics helpp

Q: An object is in equilibrium and has forces F1 = 3i+2j, F2= -2i + 4j and F3 = ai + bj N acting on it.

Find magnitude and bearing of force of F3

What i did so far:
F3= -i - 6j

I drew out the triangle where i got magnitude as root 37
But i got the bearing question wrong. Could someone help!

Thank you