Answer:
Option B. 
Step-by-step explanation:
we know that
The volume of a cone is equal to

Solve for the radius r
That means-----> isolate the variable r
Multiply by 3 both sides

Divide by
both sides

square root both sides

40 + 30s = 220
30 for each student (s) and the one charge of 40 would get the tutor 220 dollars.
Independent variable is 5 means x = 5
solve for f(x) when x = 5
f(5) = -2(5) +1
f(5) = -10 + 1
f(5) = -9
Solution (5,-9)
Answer
B. (5,-9)
One solution A. Thats the correct answer
P(t)=500(1+4t/(50+t^2 ))
P'(t) = 500 [(50+t^2).4 - 4t.2t]/(50+t^2)^2
by the quotient rule
500 (-4t^2 + 200)/(t^2 + 50)^2
Hence
P'(2) = 500 . (-16 + 200)/54^2 ~= 31.6