Points:

prob 2: 3 points
prob 3: 3 points
prob 4: 4 points

Grading Scheme:

A: Keyboard handler not working, or missing some parts (-1)
B: Clipping doesn't work for non-intersecting lines (-1)
C: No problem 3 (-3)
D: No problem 4, or it doesn't work at all (-4)