Step-by-step explanation:
Hello! Remember you have to write complete questions in order to get good and exact answers. Here you have provided neither the graph nor the equation, so I could help you providing my own graph and equation. From physics, we know that speed, time and distance are related in the following form:

So
is the slope of a line that passes through the origin where
matches the y-axis and
matches the x-axis. So we can write:

From the graph, we can know that:

And the equation that I provide is:

If both speeds are given in mi/h, then by comparing them, we can say that the speed (rate) of the first car (graph) is 20mi/h less than the speed of the second car (equation)