Question 246548
You can have a decimal as the slope. It often is.
You have to subtract y's and x's

The y's are 7 and -12
The x's are 5 and -7
the rise y's are  the numerator and  the run the x's are the denominator
your answer is correct but you made a mistake in setting it up.
you started with the second point 
(-12-7)/(-7-5)=-19/-12

You forgot the minus in the 7 of the denominator otherwise it would be +2 and not -12