A door (3 ft tall and 2 feet wide) is located in the side of a tank and is hinged along its bottom edge. A pressure of 100 lbf/ft2 is applied to the liquid free surface of the tank, and the top of the liquid free surface aligns with the top of the submerged door. Find the force required to keep the door closed. The specific weight of the liquid is 100 lbf/ft3.