ok basically slope can be found by doing one y value - the other y value divided by one x value - the other x value. so in this it would be (18-6) divided by (5-3) which is 12 divided by 2, which is 6. So slope = 6.
6 = 6(3) + b
6 = 18 + b
-12 = b
f(x) = 6x-12