Question 6553
The formula to find the slope which you should use for these types of questions is:

(y2-y1)/(x2-x1)

where y2 is the second y coordinate and y1 is the first y coordinate (the same rule applies for x2 and x1).

Thus,

a) (0-8)/(3-9) = 8/6 = 4/3
b) (-9+4)/(4+4) = -5/8

Hope that helps.
Regards,
-Mike