Study the dependence of water vapor pressure on temperature.  Make a
graph that shows the relation of temperature and vapor pressure.  That
is to say, show the points given below on a temperature vs. pressure
plot and connect them with a smooth continuous line (curve). 
Equivalently, find an algebraic equation that describes the vapor
pressure as a function of temperature.  Make a second graph, or
algebraic function, that describes height (above sea level) and
atmospheric pressure (during a normal, quiet day).  Use these two
graphs (relations) to create a new graph and relation (equation)
showing the dependence of height and water boiling temperature (for a
normal day that is).  Determine the height where water would boil at 0
degrees, i.e.:  ice would become boiling water!  Mention the slope of
your final graph at these heights:  1, 2, 5, 10, 15, and 20 km.  What
wouild the boiling temperature be at the top of a tall, say 100m,
building?  Propose a design of an altimeter (height measuring device)
using a thermometer.  Comment on the shape of your graph.  Can you
suggest an equation for your final curve?

I don't think I want to do the whole job for you but here are the raw materials.
The Clausius-Clapeyron equation expresses vapor pressure vs temperature
(and other things)  Use "Clausius-Clapeyron equation" and Google will guide
you to several tutorial sites.

Again, Google, using "Pressure vs Altitude" provides you with the exponential
relaitonship between them (we remember from school, 10,000 feet is 1/2 the
pressure and believe it when we climb to such altitudes or fly)

Put those together in the way you want and you will have it..
Thanks for making me think about these things again.
kk