A vessel with square cross-section and height of 6 m is vertically partitioned. A small window of $100c{m^2}$ with hinged door is fitted at a depth of 3 m in the partition wall. One part of the vessel is filled completely with water and the other side is filled with the liquid having density $1.5 \times {10^3}kg/{m^3}$. What force one needs to apply on the hinged door so that it does not get opened ?
(Acceleration due to gravity $ = 10m/{s^2}$)