Two polygons are similar if these two facts both must be true:
 Corresponding angles are equal.
 The ratios of pairs of corresponding sides must be equal.
(in other words, if they are proportional).
The symbol for "is similar to" is
If these two shapes are similar, what is the measure of the missing length b?
The corresponding sides of similar shapes are proportional.
The trapezoids' longer sides have a ratio of , which is
.
The trapezoids' shorter sides have a ratio of
.
Write a proportion:
Find the cross products and solve:
42 
= 
14b 

42 ÷ 14 
= 
14b ÷ 14 

3 
= 
b 
The missing length is 3 kilometers.