algebra, 12/6

a-c block:   1) m230, # 5-10 and 20-26 (all using rise/run)
                  2) m230, #27-34 (using y2-y1/x2-x1)

d-block:   1) b170, #4-15
                2) m245, # 46, 47, 52-58, 62-65