11. Parallel lines have the same slope, so the slope of EF is the same as the slope of CD. The slope of CD is found as
.. slope = (difference of y coordinates)/(difference of x coordinates)
.. = (9 -1)/(-1 -(-7)) = 8/6 = 4/3
The slope of EF is ...
.. B. 4/3
12. The perpendicular line is vertical. Its slope is ...
.. D. undefined