Problem $8($Halliday Problem $12\mathrm{.}17)$

In Fig. $12-34,$ a uniform beam of weight $500$ N and length $3\mathrm{.}0$ m is suspended horizontally. On the left it is hinged to a wall; on the right it is supported by a cable bolted to the wall at distance $D$ above the beam. The least tension that will snap the cable is $1200$ N $.($a$)$ What value of $D$ corresponds to that tension? $($b$)$ To prevent the cable from snapping, should $D$ be increased or decreased from that value?