algebra, 1/17

a-c block:    b170, #7-15
                   b171, # 18-20
                   for all problems, write rise/run = , y-intercept=, AND graph

d-block:     b212, # 7-9 (just isolate one variable)
                  b212, #10-15 (solve the system using substitution)
                  b213, # 18-20