Let
t = time, hours
h = height, feet
At 1 PM, the time and height are respectively
t₁ = 1 hour
h₁ = 4400 feet
At 4 PM, the time and height are respectively
t₂ = 4 hours
h₂ = 5600 feet
By definition, the mean hourly change in elevation is

Answer: 400 feet per hour
He rents for d days, but two days are free, so he pays for only d - 2 days.
The rental fee is $45 per day, so for d - 2 days, he pays 45(d - 2). The total he pays is $315, so the equation is
<u>45</u>(<u>d</u> - <u>2</u>) = <u>315</u>
Now we solve the equation to find d, the number of days.
45(d - 2) = 315
45d - 90 = 315
45d = 405
d = 9
The number of days is 9.
The answer is $12.50 per cd .