The line of action of the force is 30 cm from joint A. Therefore, the magnitude of the bending moment is

     M_A = F d_A

           = (80 N) (30 cm) = 2,400 N-cm

The distance from joint B to the line of action of F is found from the Pythagorean theorem:

     d_B = (30² + 45²)^0.5 = 54.08 cm

Substitute and solve for the magnitude of the moment:

     M_B = (80 N) (54.08 cm) = 4,327 N-cm

Calculate the moment arm and the moment at joint C in the same manner as for joint B:

     d_C = (15² + 45²)^0.5 = 47.43 cm

     M_C = (80 N) (47.43 cm) = 3,795 N-cm

Calculate the moment of F at joints D and E in the same manner as for joints B and C:

     d_D = (15² + 15²)^0.5 = 21.21 cm

     M_D = (80 N) (21.21 cm) = 1,697 N-cm

     d_E = (30² + 15²)^0.5 = 33.54 cm

     M_E = (80 N) (33.54 cm) = 2,683 N-cm

The joint with the largest moment is joint B, which has a moment of 4,327 N cm, or in more common units 43.27 N-m.