Statics: Determine the fourth force

The 100-lb resultant of four forces together with the three of those four forces is shown. 
Determine the fourth force (P).

Rx = 100 cos45º = 70.71 lb
Ry = 100 sin45º = 70.71 lb


→+ΣFx = 70.71     
-70cos60º - 120cos60º + 50cos50º + Px = 70.71
Px = 133.571 lb


↑+ΣFy = 70.71
-70sin60º - 120sin60º -50sin50º + Py = 70.71
Py = 152.313 lb

P² = Px² + Py²

P² = (133.571)² + (152.313)² 

^{P = 202.58 lb}

for theta (θ)

tan(θ) = 152.313 / 133.571

θ = 48.75º