What is the slope of (3,-20),(5,8)

The equation for slope is y² - y
                                        x² - x

So it would be:                8 - (-20)   or    8 + 20
                                          5 - 3               5 - 3 

28
 2

Then, you have to reduce it, divide both by two.
 
 14
  1

Since it is over 1, then it is just the numerator.

Your final is:
Slope = 14