Answer:
Step-by-step explanation:
Let
x----> the length of the rectangular garden
y---> the width of the rectangular garden
we know that
The perimeter of the rectangle is equal to
we have
so
simplify
------> equation A
Remember that the area of rectangle is equal to
----> equation B
substitute equation A in equation B
----> this is a vertical parabola open downward
The vertex is a maximum
The y-coordinate of the vertex is the maximum area
The x-coordinate of the vertex is the length side of the rectangle that maximize the area
using a graphing tool
The vertex is the point 
see the attached figure
so
Find the value of y
The garden is a square
the area is equal to
----> is equal to the y-coordinate of the vertex is correct
<h2><em><u>
Answer:</u></em></h2>
Total Surface Area = 375 
<h2><em><u>
Step-by-step explanation:</u></em></h2>
You need to find the area of the ceiling, floor, the two rectangle walls and the two trapezoid walls
<u>Area of the ceiling:</u>
c = length * width
c = 9*6.5 = 58.5
<u>Area of the 2 rectangle walls:</u>
w = 2(length * width)
w = 2(9 * 8)
w = 2(72)
w = 144
<u>Area of floor:</u>
f = 9 * 7.5
f = 67.5
<u>Area of the two trapezoids:</u>
a = 6.5
b = 7.5
h = 7.5
Total Surface Area = c + w + f + t
Total Surface Area = 58.5 + 144 + 67.5 + 105
Total Surface Area = 375
