b$)$ A vertical dock gate, $7m$ wide, has a water depth of $11\mathrm{.}5m$ on one side

and a depth of $7\mathrm{.}5m$ on the other side as shown in Figure $3\mathrm{.}1$ below. Find the resultant force on the dock gate and the position of its line of action.

Figure $3\mathrm{.}1$