The border will have 20 squares two times, and 24 squares two times as well, that is the perimeter or the border, because a quilt has 4 sides:
20*2 + 24*2 = 40 + 48 = 88
So the border will have 88 squares total. So if the border can have only one design, Lu can use any toy design 88 times if she wants the border to have the same toy design in it.