I have seen you ask this question twice before, so I will give you the answer that HugoD gave you:
In mathematics, "of" is translated as a multiplication.
So, you have :

.
Percentages are numbers that are units of 100
The value of 20% of 80 is 16
<h3>How to determine the percentage value</h3>
The model is not given.
However, the percentage value can still be calculated
The expression is given as:

Express of as product

Express 20 % decimal

Evaluate the product
16
Hence, 20% of 80 is 16
Read more about percentages at:
brainly.com/question/843074
Answer:
133 ft
Step-by-step explanation:
Given in the question,
length of the rectangle = 31 ft
width of the rectangle= 20 ft
diameter of semicircle = 20 ft
radius of semicircle = 20/2 ft = 10 ft
Formula to use:
<h3>perimeter of rectangle + perimeter of semicircle</h3>
perimeter of rectangle = 2(l+w)
perimeter of semicircle = 1/2(2πr)
Plug values in the formula above
2(31 + 20) + 3.14(10)
133.4 ft
≈ 133 ft