Answer:
the y intercept is -9/2 or -4 1/2
If the recipe makes enough stew for 6 people, and the ingredients cost $9.75, then for 24 people it will cost $x. You can write this statement as
6 people - $9.75,
24 people - $x.
Or as proportion,

Find x:

Answer: It would cost $39 to serve 24 people
Sorry this took so long! I managed to do everything except for the parts involving standard deviation. (I tried but I couldn't quite figure it out.)
~Hope this helps!~
Given:
Current revenue = $6000
<span>R(f)= -100f^2 + 400f + 6000
where f is a whole number of $5 fee increases
We are told to find f, when R(f) </span><span>< 6000
Since </span>R(f)= -100f^2+400f+6000
R(f) < 6000 ⇒ -100f^2+400f+6000 < 6000
Subtract 6000 from both sides
-100f^2 + 400f + 6000 - 6000 < 6000 - 6000
-100f^2 + 400f < 0
⇒ 400f - 100f^2 < 0
Divide the equation by 100
400f/100 - 100f^2/100 < 0/100
4f - f^2 < 0
Add f^2 to both sides of the equation
4f - f^2 + f^2 < 0 + f^2
4f < f^2
Divide both sides by f
4f/f < (f^2)/f
4 < f
⇒ f > 4
⇒ f ≥ 5
Therefore, <span> for 5 or more numbers of $5 fee increases, the revenue from fees will actually be less than its current value.</span>