Answer:
Therefore the width is 25 feet for getting maximum area.
The maximum area of the rectangle is 625 square feet.
Therefore the range is 0≤A≤625.
Step-by-step explanation:
Given function is
A = - x²+50x
We know that ,
If y = ax²+bx+c
For the maximum 
Here a = -1 , b= 50 and c=0
Therefore the width 
Therefore the width is 25 feet for getting maximum area.
The maximum area =[ -(25)²+50.25] square feet
= 625 square feet
The area can not be negative and maximum area is 625 square feet.
Therefore the range is 0≤A≤625.
It's three the m means nothing in this case
Firstly setup an equation to find the perimeter:
3x + 4x + 5x = 54, this is because perimeter is equal to sum of all side lengths
Then combine like terms:
12x = 54
Now use the division property of equality by dividing both sides by 12:
x = 4.5
So then, you will substitute the value of x for each value of the side lengths:
3(4.5) = 13.5 for AB, 4(4.5) = 18 for BC, and 5(4.5) = 22.5 for AC.
Hope this helps and let me know if you have any more questions!