The rectangle on a coordinate plane with a perimeter of 18 units is added as an attachment
Drawing a rectangle on a coordinate plane
From the question, we have the following parameters that can be used in our computation:
The incomplete figure of a rectangle (see attachment)
Also, we have
Perimeter = 18 units
Also from the figure, we have the given side length to be
Width = 3 units
Using the formula of perimeter, we have
Perimeter = 2 * (Length + Width)
By substitution, we get
2 * (Length + 3) = 18
Length + 3 = 9
This gives
Length = 6
So, the missing side must have a length of 6 units
The figure is attached