Answer:
r = 4
Step-by-step explanation:
Calculate the slope m using the slope formula and equate to 5
m = (y₂ - y₁ ) / (x₂ - x₁ )
with (x₁, y₁ ) = (7, r ) and (x₂, y₂ ) = (8, 9)
m = =
= 9 - r = 5 ( subtract 9 from both sides )
- r = - 4 ( multiply both sides by - 1 )
r = 4