What is the constant of variation for the subscription cost based on the number of weeks

There exists the same question with the following choices:

A. $1.50

B. $7.50

C. $15.00

D. $30.00

The correct answer to this question is letter B. $7.50. By definition, a constant of variation is the number that relates two variables that are directly proportional or inversely proportional to one another. So, in this problem, which supposedly have a graph, the constant of variation is 7.50