really simple. Just input several x values into the equation t get the y values (output) for example if x=1 then y= 3(1) -1 which is 2. So one of your coordinates would be (1,2).
Let's say we want to find when x=5. Then y would be y=3(5)-1 which would be 14. Our next coordinate to graph would be (5,14)
Hope I helped!
