Answer:
The dimensions are 9m by 18 m
Step-by-step explanation:
The perimeter will be
x+y+x for the three sides ( the wall is the fourth side)
2x+y = 36
Solving for y
y = 36-2x
The area is x*y and we want it maxed
A =x( 36-2x)
36x-2x^2
Taking the derivative
dA /dx = 36 - 2 * 2x
Setting this equal to zero to find the max
0 = 36 - 4x
4x = 36
Divide by 4
x = 36/4
x = 9
Now find y
y = 36-2x
y = 36 - 2*9
y = 36 - 18
= 18
The dimensions are 9m by 18 m
