Answer:
It would be slightly higher than 8.5 and lower than 9.
Step-by-step explanation:
8.6 is bigger than 8.5, but it's smaller than 9, so you would place it in between the two but closer to the 8.5 mark.
The answer to the question
Given:
The area of the rectangular garden is 18z+24 sq ft.
To find the possible dimensions of the garden.
Formula
The area of the rectangular garden is

where,
l be the length of the rectangle
b be the width.
Let us take l and b be the length and width of the given rectangular park respectively.
Now,
According to the problem,

or, 
We can determine that,
l = 6 and b = 3z+4 or vice versa.
Hence,
The possible length and width of the rectangular garden is 6 and (3z+4) respectively.