y = - 13 + 3x
1) the equation is a striaght line with y-intercept - 13 and slope 3
2) the horizontal axis is x, number of hours.
3) the vertical axis is y, temperature measured in °F
4) y-intercept = - 13=>: point (0, - 13)
5) x - intercept: y = 0 => x = 13/3 => point (13/3 , 0)
With all that information you can draw the graph easily.