The graph shows how many bottles a machine caps in a certain number of seconds. A graph showing number of bottles capped on the y axis and number of seconds on the x axis. A line begins at the origin and passes through the points 15 comma 300, 30 comma 600, and 45 comma 900.

Part A
What is the constant of proportionality, and what does it mean in this situation?
Use the drop-down menus to show and explain your answer.