Answer:
The Slope is 9 and the y-intercept is -2
Step-by-step explanation:
To answer this question we can propose the following equation:

Where:
x is the number of weeks elapsed.
d is the debt depending on the weeks.
Robert promised to pay at least $ 67 each week.
Therefore, after 5 weeks the debt of rober should be:


Then scenario A) is possible because
.
After 6 weeks:


Then scenario B) is possible because
.
After 7 weeks


Then scenario C) is possible because
.
After 8 weeks


So scenario D) is NOT possible because 
Finally the correct answer is option D.
Answer:
4
Step-by-step explanation:
It's AoPS question
4n - (7-6n)
4n -7 +6n (multiply minus to 7-6n)
10n -7 is the answer
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.