Answer:
Width=20 feet
Since Length=Width=20 feet, the rectangle is a Square.
Step-by-step explanation:
Area, 
To determine the width of the rectangle that gives the maximum area, we take the derivative of A and solve for its critical point.

The width of the rectangle that gives the maximum area =20 feet.
Perimeter of a rectangle=2(l+w)
Perimeter of the rectangle=80 feet
2(l+w)=80
2l+2(20)=80
2l=80-40
2l=40
l=20 feet
Since the length and width are equal, the special type of rectangle that produces this maximum area is a Square.
https://www.khanacademy.org/math/precalculus/prob-comb/combinatorics-precalc/v/permutation-formula
I would watch a bunch of videos or ask a teacher or something for help
I'm guessing the second derivative is for <em>y</em> with respect to <em>x</em>, i.e.

Compute the first derivative. By the chain rule,

We have


and so

Now compute the second derivative. Notice that
is a function of
; so denote it by
. Then

By the chain rule,

We have

and so the second derivative is

Answer:
57,000,000
Step-by-step explanation:
1. Sum the numbers 34,000,000 + 23,000,000= 57,000,000