How can i better understand how to do this?

1.5 cm/s

Step-by-step explanation:

The graph shows the speed of a worm as a relationship between the distance it can travel in centimeters over time, or seconds.  Since the graph forms a straight line, then we know that the speed of the worm is constant over time, meaning that he will move the same distance each second.  Given the point (6,9) on the graph, this tells us that the worm moved 9 centimeters in 6 seconds or:

So, the ratio of centimeters over seconds is 9/6.  However, unit rate is the distance every second or putting the ratio over '1'.  We can do this by diving the numerator by the denominator or 9 ÷ 6 = 1.5 centimers/second.