Respuesta :

I think the answer is R² = P² + Q² - 2PQ Cos θ ; where P = 72 lbs, Q = 56 lbs and θ = 37° 
R² = 72² + 56² - 2*72*56*Cos 37 
R² = 72² + 56² - 2*72*56*Cos 37 
R² = 14,760.196 
R = 121.49 lb ----- So Answer should be (C)