The irregular shaped tank is drained through a $135-$mm diameter orifice in the base of the tank. The coefficient of discharge for the orifice is $0\mathrm{.}64.$ The diameter of the $3\mathrm{.}2-$m high tank varies uniformly from $1\mathrm{.}2$ m at the base to $1\mathrm{.}5$m at the top. Determine how long it would take for the depth of water in the tank to drop from $2\mathrm{.}9$ m to $0\mathrm{.}9$ m$.$