Answer: 0
Explanation:
Y2 - Y1
________.
X2 - X1
A linear slope means that the Ys are the same and you can't divide by zero.
You have your points (8,7) and (3,7)
Use the template like I have above.
7 - 7
______
3 - 8
which equals....
0
__
-5
I hope that makes sense for you :)