x = # of hours the bike was rented.
$40 = $12 + $7x
Subtract $12 from both sides.
$28 = $7x
Divide both sides by $7
4 = x
Sandy rented the bike for 4 hours.

Differentiate both sides, treating
as a function of
. Let's take it one term at a time.
Power, product and chain rules:



Product and chain rules:




Product and chain rules:




The derivative of 0 is, of course, 0. So we have, upon differentiating everything,

Isolate the derivative, and solve for it:


(See comment below; all the 6s should be 2s)
We can simplify this a bit by multiplying the numerator and denominator by
to get rid of that fraction in the denominator.

The value of the length DF is 1/4 of that of CD because of the Angle Bisector Theorem for triangles.
<h3>
What is the Angle Bisector Theorem?</h3>
The Angel Bisector Theorem states that if a ray bisects an angle of a triangle, it dissects the side of the triangle that is opposite to the dissected angle into parts that are proportionate to the adjacent sides.
Note that the angle that has been dissected here is ∠CBD. Thus,
= 
See the link below for more about Angle Bisector Theorem of the Triangle:
brainly.com/question/21475560
Answer:
41.6666667?? I didnt know if you needed is simplified .-.