The function you're given is in point-slope format, which is one of the easiest ones to graph. The basic form of the format is;
y=ax+b
Where a is the slope and b is the y-intercept.
As you can see, in y=-13+3x, the positions of a and b are switched, but it is essentially the same question.
From here we can tell that the y-intercept is -13, meaning that there is a point on the line that rests at (0,-13)
To find the other points, we can do rise-over-run using the slope of 3 given to us. What happens here is that for every 1 unit you go to the right (positive), you rise 3 units up.
For example, if we perform this on the y-intercept (0,-13):
(0+1, -13+3)
(1,-10)
With these two points, you can graph the line representing the temperature.
