The constant of proportionality refers to the constant value of the ratio of two proportional quantity A and B which is usually written in the form of B = KA, where K is the factor of proportionality and is constant.
In the question given above, the constant of proportionality is 24. To determine the constant of proportionality, look at the graph and take note of each price and the number of video it can send.
From the graph, it can be seen that, 48 cents will send 2 video messages, 96 cents will send 4 messages, 144 cents will send 6 messages and 192 cents will send 8 messages.
48/2 = 24
96/4 = 24
144/6 = 24
192/8 = 24.
