Answer:
r= 3b
Explanation:
We can find the slope of the line by using
m= (y2-y1) /(x2-x1)
= (12-9)/ (4-3)
= 3/1
The slope is 3
We can use the point slope form for the equation of a line
y-y1 = m(x-x1)
y-12 = 3(x-4)
Distribute the 3
y-12 = 3x-12
Add 12 to each side
y -12+12 = 3x-12+12
y= 3x
let r =y
and x=b
r = 3b