Answer:
r = 1
Explanation:
Calculate the slope m using the slope formula and equate to

m =

with (x₁, y₁ ) = (- 1, - 3) and (x₂, y₂ ) = (7, r)
m =
=
=
( cross- multiply )
2(r + 3) = 8 ← distribute left side
2r + 6 = 8 ( subtract 6 from both sides )
2r = 2 ( divide both sides by 2 )
r = 1