 When we talk about pressures, a useful tool is recognizing how pressures at the same height within a column of the same fluid are affected by pressure increases. Pascal's law says that the pressure applied to a confined fluid increases the pressure throughout by the same amount. So if we were to look at this situation, where the force at 1 and 2 are both increasing the pressure of the fluid here, we can describe the pressure at any arbitrary height as being the same on both the left and the right sides. It doesn't matter that the cross-sectional areas are different. The pressure increases everywhere, so as long as you are at the same height, you will have the same pressure. Pascal's law is very useful when we are analyzing monometers as well as any sort of hydraulic system.