Figure 1 depicts an arm holding a ball in static equilibrium. Figure 2 shows the free-body diagram of the lower arm where F is the force applied by the biceps muscle at an angle of θ = 60 degrees with respect to the lower arm, and R₁ and R₂ are the reaction forces acting at point O. The weights of the ball and the lower arm are W₁ = 50 Newtons (N) and W₂ = 20 N, respectively. The force exerted by the biceps muscle is F = __________ N. (Round off to the nearest integer). Assume the lower arm to be a rigid body.