$7\mathrm{.}58$ For the beam and loading shown, determine $($a$)$ the distance a for which the maximum absolute value of the bending moment in the beam is as small as possible, $(b)$ the corresponding value of $|M{|}_{\text{m}\text{a}\text{x}}.($See the hint for Prob. $7\mathrm{.}55.)$

Fig. P$7\mathrm{.}58$