The perimeter of the figure is 20 inches. what is the missing side length?

You would do the whole perimeter (the length of all the sides added up) minus the three known sides to find the missing side.
20 - 4 - 4 - 8 = 4, so the answer would be 4 inches.

When finding perimeter you add all the sides up.
So if you're looking for the perimeter, which is 20, just add 8 + 4 + 4
That equals 16.
So do 20 - 16.
Then you get your answer which is 4 in

You could also do:
20-8
That's 12
Then 12-4
That's 8
Then do 8-4
To get you your answer of 4 in

Okay i will add you