Question 442692
You are given two points:  (9,12.5)  (-9,3.5)

12.5 - 3.5
----------
9 + 9 

9/18 = 1/2

{{{y - 12.5 = expr(1/2)(x-9)}}}
{{{y -12.5 = expr(1/2)x - expr(9/2)}}}
{{{y = expr(1/2)x - expr(9/2) + expr(25/2)}}}
{{{highlight(y = expr(1/2)x + 8)}}}