Physical Chemistry question: If 2.0 x 10^23 argon (Ar) atoms strike 4.0 cm^2 of wall per second at a 90 degree angle to the wall when moving with a speed of 45,000 cm/s, what pressure (in atm) do they exert on the wall? The answer to this question is in the back of the book, but I cannot figure out how to get there.