Add my answer to Exercise 4.15.

Included are the following 2 files:

	Exercise_4.15.pdf
	Exercise_4.15.tm

Thank you!
							Lawrence X. Amlord
							  Feb 3rd, 2014
							  Fuzhou, China
Add my answer to Exercise 4.16.

Included are the following 2 files:

	Exercise_4.16.pdf
	Exercise_4.16.tm

Thank you!
							Lawrence X. Amlord
							  Feb 7th, 2014
							  Fuzhou, China