You've got two right triangles. Use Pythagorean theorem:
Expand the brackets and subtract the first equation from the second one:
Now plug in the given value for b and solve for a. I've got a = 16.9. Thus d = 6.25.
You now have all values to calculate the angles at B.
I asume that you know how to add forces and that you need a parallelogram to get all partial forces.