Is y equals 9 plus 3x linear?

Answer 1

y=9+3x is linear because there is only one value of x so it will go up proportionally, for instance if x=1 then y=12, x=2 y=15, x=3 y=18.

they will always go up by three, only equations with multiple xs, eg x squared+4x+6 is non linear and x cubed-9 is non linear.