Answer:
A.

Explanation:
(0,0)
(5,-1)
0,5 - x-coordinates
0,-1 - y-coordinates
x-coordinates are bold, y-coordinates not bold
calculating slope, we create a fracture
in numerator we insert y-coordinates: first normal and second one with an opposite sign
in denominator we have x-coordinates: first normal and second one with an opposite sign
