The slope of the tangent line to
at
is given by the derivative of
at that point:

Factorize the numerator:

We have
approaching -1; in particular, this means
, so that

Then

and the tangent line's equation is

1 gallon = 4 quarts.
15 quarts/ 4 = 3.75 gallons
1 hour = 60 minutes
3.75 gallons / 60 minutes = 0.625 gallons per minute.
I think C is the answer.
In the box, everything is evened out and nothing is bigger than the other.
So, your answer:
C