hw_lect15_1: 2 points;  1 point for each part; 0.5 partial are given if showing process. 

hw_lect15_4 (include 16_1) : 5 points; 1 point for each part; 0.5 partial are given if showing process. 

hw_lect16_3: 1 point for completion 

7.4: 1 point for completion 

hw_lect17_2: 1 point for completion