Figure I and Figure II are similar quadrilaterals.

figure one
trapezoid
8.5 for sides
10 for the top
11 for the bottom

figure 2
trapezoid on its side
4.25 for the sides
5 for the top
x for the bottom

which proportion must be true?

10/5 = 11/b

10/5 = b/11

8.5/5 = b/8.5

10/b = 11/5