Update Exercise 1.27.scm
Add my answer to Exercise 1.28.

Included are the following 4 files:

	Exercise_1.28.pdf
	Exercise_1.28.scm
	Exercise_1.28.tm
	Test_for_Exercise_1.28.scm

Thank you!
							Lawrence R. Amlord
							   May 7th, 2013
							   Xi'an, China