An open rectangular tank is $2m$ wide and $4m$ long. The tank contains mercury $)=(13\mathrm{.}6$ to a depth of $2m,1\mathrm{.}5m$ depth of water and oil $)=(0\mathrm{.}8$ on top of the water to a depth of $1m.$ Determine the magnitude of the resultant fluid force acting on the base the tank.