add solution to Exercise 6.1-4.

Included are the following 2 files:

	6.1-4.pdf
	6.1-4.tm

Thank you!
							Lawrence X. Amlord
							  Jun 11st, 2014
							  Xi'an, China
add solution to Exercise 6.1-5.

Included are the following 2 files:

	6.1-5.pdf
	6.1-5.tm

Thank you!
							Lawrence X. Amlord
							  Jun 11th, 2014
							  Xi'an, China
add solution to Exercise 6.1-6.

Included are the following 2 files:

	6.1-6.pdf
	6.1-6.tm

Thank you!
							Lawrence X. Amlord
							  Jun 11th, 2014
							  Xi'an, China