$($a$)$ Draw the influence line for force in member $CD,$ and then $($b$)$ determine the maximum force $($both tension and compression$)$ that can be developed in this member due to a uniform live load of $12k\frac{N}{m}$ which acts along the bottom cord of the truss.

Fcd at $9$m$?$ why $0\mathrm{.}75?$ i solved

x$>=9$

moment G $=0$

$-$ay$(6$m$)+$fcd$(3$m$)=0$

$($Ay$=(12-$x$)/12)$

x$=9->$Fcd$=0\mathrm{.}5$

why $0\mathrm{.}75?$