Please change the statement of Solution/Exercise 5-8 on page 160 of Math Proofs Demystified to read as follows.

SOLUTION/EXERCISE 5-8

Try this for yourself, taking advantage of an additional postulate: "Given two parallel lines that are transversal to two other parallel lines, the pairs of corresponding parallel line segments have equal lengths." The proof then follows from the "combined forces" of Solution 5-6 and Solution/Exercise 5-7.