Compute the force necessary to keep the door close

A tank with a square base of area 1.0 {{m}^{2}} is divided by a vertical partition in the middle. The bottom of the partition has a small hinged door of area 20 {{cm}^{2}}. The tank is filled with water in one compartment and an acid (of relative density 1.7) in the other, both to a height of 4.0. Compute the force necessary to keep the door close.