The force on a specific point on the glass depends upon the depth of that point- so consider a line across the window having all points at depth "h". The force thin "rectangle", L by dy, L the length of the line across the wind, dy the "infinitesmal" thickness of the rectangle, on that line is the weight of the water above it which is where is the density of salt water. Take y measured vertically from the top of the window. What is the width, L(y), of the window at that y? What is the depth, h(y)?

The total force is given by where Y is the distance, vertically, from the top of the window to the bottom. You will need to take that 30 degree angle into account.