Next I add these two equations together and

when I do that the pressure at the interface P1 cancels

out that leaves me with P2 minus P0 equals is to minus

gamma gasoline Z1- Z0 minus gamma water Z2 minus Z1.

Or rearranging, the pressure at the bottom, P2.

P2 is equal to the pressure at the top,

P 0, plus the pressures due to the two columns of liquids,

gamma G times Z node minus Z1 plus gamma water Z1 minus Z2.

In other words, very simply, all we do

is add the pressures due to each column of fluid when we have different fluids.

So, in this example, if the specific gravity of gasoline is 0.68,

I'll leave you to do these calculations such an example.

The pressure at the bottom here P2 is 6.31 psi.

In other words pounds per square inch gauge above atmospheric pressure.

If we have a single fluid, the equation is even more simple, and in this case,

the pressure here is just equal to the pressure due to the column of fluid here,

which is Gamma 1 times h 1 plus the pressure at the open surface here,

which is atmospheric pressure.