add solution to Part a. in Problem 6-2.

Modified is the following file:

	6-2.tm

Thank you!
							Lawrence X. Amlord
							  Jun 28th, 2014
							  Xi'an, China
add solution to Part b in Problem 6-2.

Modified is the following file:

	6-2.tm

Thank you!
							Lawrence X. Amlord
							  Jun 29th, 2014
							  Xi'an, China