Answer:
r = -1
Step-by-step explanation:
(y2-y1)/(x2-x1)=m
(r,7)=(x1,y1) and (3,4)=(x2-y2) and m=-3/5
so plug in...
(4-7)/(4-r)=-3/5
then solve for r which will get that r = -1
numerator: 4-7=-3
denominator: 4-r=5 -> 4-5=0+r -> -1=r
