The question is poorly worded! I just discussed this with my wife who is a quilter. In quilting there is a difference between border and binding(DAMHIKT). On a quilt 3 units by 4 units, a binding would be 14 units whereas a border would require 18 units or blocks. The binding just goes around the outside edge: 4+3+4+3=14 (the perimiter) whereas a border uses those 14 plua 4 additional units since you have to fill in the corner spaces.
Obviously, whoever wrote the question is not a quilter. To bad the concepts of perimeter, circumfrence, etc are foreign to the present educational system!
Your wife is correct, it’s 18.