The other tutor used the formula.  Here is the GRAPHICAL method.



Start at the lower point and draw a vertical line upward until it is
exactly right of the upper point:




That's the RISE. Count the blocks that make up its length, which is 10
units.  It goes up, so its value is POSITIVE.  So the RISE = +10.


Now start where the green RISE stopped and draw a horizontal line 
leftward until it is on the upper point:



That's the RUN. Count the blocks that make up its length, which is 12
units.  It goes LEFT, so its value is NEGATIVE.  So the RUN = -12

SLOPE =  =  = 

Edwin