Determine maximum bending stresses

Constructing the shear diagram

Considering the segment
from x = 3 m to x = 4 m

     area under
               load = -20.00 kN
     concentrated
             forces =   0.00 kN
     total shear
              force = -20.00 kN

        at x = 3 m,    V =   +20.00 kN
           total shear
                  force   =   -20.00 kN
        at x = 4 m,    V =      0.00 kN