So here's the sort of thing I am dealing with in chem class:

A spherical balloon with a radius of 120 meters:
Twenty students want to go for a ride in the balloon and they
weigh an average of 150 pounds (453.6g/pound).  The total mass
besides the people is 82 kg.  The balloon flies on helium and nitrogen
gas, with a .80 mole fraction of helium.  The internal temperature
of the balloon is 16 degrees Celsius, which is the same as the
surrounding air.  When the external pressure  is .80 atm, and the
balloon is floating, what is the internal pressure of the balloon?  The
molar mass of the air is 28.92g/mol.  (The volume of a sphere
is: 4/3*pi*(r^3).)

OK, so post your answers, folks! :)