Explanation:
Remember the y = mx + b form! M is the slope while b is the y-intercept. So it is already given from the problem that m is 1/3 so:
y = 1/3x + b
Plug the -3 in for x and -6 in for y. What value does b have to be then?
-6 = 1/3(-3) + b
-6 = -1 + b
b = -5
b has to be -5! So the equation for all points is:
y = 1/3x - 5