$(40$ points$)$ A $30-m-$long vessel, with a cross$-$section shown in the figure below, carries a

load of $6000$ kN $.$

$($a$)(20$ points$)$ Find the distance $($D$)$ from the top of the vessel to the liquid top level if the

vessel mass is $120000$ kg and the liquid has a specific gravity $(S)$ of $1\mathrm{.}4.$

$($b$)$ points$)$ Is the vessel stable? The center of gravity $(G)$ of the combined vessel and

load is located as shown below.