Whoops.. too early in the morning to be doing SAT problems
Here's a new (hopefully correct) explanation:
0 = p^2-4 => p = 2 or -2 => point A = (0,2) or (0,-2)
5 = t^2-4 => t= 3 or -3 => poing B = (5.3) or (5,-3)
Like gcf101 said, instead of calculating all the slopes, it would probably be easier to plot the four points and look for the pair with the highest (steepest) slope.