Answer: 3 mi/h
Step-by-step explanation:
Here we have to find the speed 
at which Sarah walks to school, knowing the distance 
she has walked and the time 
she expends.
So, in this case we can use the following equation:
Where:
Solving:
This is Sarah's speed
2y+18=42
2y=24
y=12
Hope this helps!
Answer:
67.5
Step-by-step explanation:
4.5x6x2.5=67.5
x = number of hours after 9 am (eg: x = 1 means 1 hr after 9 am, so 10 am)
f(x) = population count x hours after 9 am
f(1) = population count at 10 am (1 hour later)
f(2) = population count at 11 am (2 hrs after 9 am)
f(2) - f(1) represents the difference in population counts from 10 am to 11 am, or put another way, how much the population increased during that time interval.
