$(1)$ Find the shear force and the bending moment on the cross section I.

$(2)$ Find the shear force and the bending moment on the cross section II$.$

$(3)$ Draw the shear force and bending moment diagrams of the beam and determine the maximum shear force and the maximum bending moment $($in the sense of the absolute value$)$ in the beam.

a$=0\mathrm{.}6$