In that equation it tells you that your slope is 2/3. It also tells you that your y intercept is -4. (Remember slope is written in y=mx+b) So first you plot your y value. (Remember that y intercept is up and down and slope is rise/fall over run) So your first point should be located at -4. Now you can began putting in your slope. Since your slope is positive, go up two and go to the right 3 times (rise/run). That's how you graph your equation.
This answer is pretty simple. you see (5,-8) and (20,y). well the 20 is 4 times the 5 on the x value so multiply the y value by 4 to get your answer which Y=-32 in the 2nd corrdenants.