Finding pressure due to a fluid

[xoxjojobxox]

Homework Statement

A test tube standing vertically in a test-tube rack contains 2.5 cm of oil (ρ=0.81 g/cm³) and 6.5 cm of water. What is the pressure exerted by the two liquids on the bottom of the test tube?

Homework Equations

P=ρgh
ρ=density of a fluid=mass/volume
g=gravity

P=F/A

The Attempt at a Solution

I don't know how to start this problem. I think I'm supposed to be using density of a fluid, I'm not sure. If that's the case, I know density of water=1000 kg/m^3

 

[jake929]

You should notice that the unit for the height of the oil is cm and the density is g/cm^3. Make sure your units are correct for the density of water. Keep in mind your equation for pressure P=ρgh is gauge pressure (relative to the pressure exerted on the top surface). How much pressure is exerted on the water by the oil. Then how much pressure does the water add to the bottom of the test tube?