Cord AB of length a is attached to the end B of a spring having an unstretched

Question:

Cord AB of length a is attached to the end B of a spring having an unstretched length b. The other end of the spring is attached to a roller C so that the spring remains horizontal as it stretches. If a weight W is suspended from B, determine the angle θ of cord AB for equilibrium.

Given:
a = 5 ft
b = 5 ft
k = 10 lb/ft
W = 10 lb

a B