Hi, this is the question I'm having problem with (I'll change the names and places)

When the World Cup was held outside Rio de Janeiro in 1956, there was much discussion about the effect the high altitude (7340 feet) would have on the athletes. Assuming air pressure decays exponentially by 0.4% every 100 feet, by what percentage is air pressure reduced from moving from sea level to Rio de Janeiro???

This question is using A = Pert, correct??

Someone helped me out and got this:

to find r:

1. ln 0.996 = 100r
2. -0.004 = 100r
3. 4 x 10^(-5) = r

Okay, so I get how to find r.

She continued, doing this:

4. P0 = Poe^(4 * 10 (-5) ) * (7340)
5. Po * 0.7456
6. = 74.56%

So I see that 7340 is t, correct??

I just don't know what she did after line 4 in order to find the answer. Line 5 and line 6, I don't know what she did. Don't you need to find A or P first??? How do you find A or P, and how do you find the answer???

This problem confused me because there seemed to be more than one unknown(??), meaning A and P. So...what does a person do??

Any help???