B$.6$ A rectangular gate $AB$ with $5m$ wide is hinged at $A$ as shown in Fig. B$\mathrm{.}6.$ The weight of the gate, $W$ is $10kN.$ A horizontal strut force $P$ of $60kN$ is applied at the top of the gate in order to hold the gate at its position. Determine the maximum depth of water, $h$ that the gate can be retained.

$(20$ marks$)$

Fig. B$.6$