Given parameters:
First point = (12, -5)
Second point = (10, -4)
Unknown:
Slope of the line = ?
Slope is simply the vertical rise divided by the horizontal distance.
Slope = 
Simply to find slope;
Slope = 
First point = (12, -5), x₁ = 12 and y₁ = -5
Second point = (10, -4), x₂ = 10 and y₂ = -4
Input the parameters:
Slope = 
= 
= - 
The slope of the line is -
Hope this answers your question :)
It is easier to understand the problem if you create a number based on the criteria and then perform the computations. I am going to choose: 111 22 33 4
There are 10 options for the first "1" and only 1 option for the other two 1's
There are 9 remaining options for the first "2" and only 1 option for the other 2
There are 8 remaining options for the first "3" and only 1 option for the other 3
There are 7 remaining options for the "4"
10 x 1 x 1 x 9 x 1 x 8 x 1 x 7
10 x 9 x 8 x 7 = 5,040
Answer: 5,040