Solve for r

Question

(1,r) (3,-5) are two points on a line with slope -4.
Find r

r = -5 - r/ 3-1

r= 3

Answer 1

m = (-5-r)/(3-1) = -4.
(-5-r)/2 = -4.
Multiply by 2:
-5-r = -8.
r = 3.