To answer the questions based on the context provided (assuming the graph depicts a linear relationship), here is how you could proceed:
a. The constant of proportionality is 15. (Assuming from the options given and a typical proportional relationship where the graph increases consistently.)
b. An equation that represents this graph is y = 15x. (This represents a direct proportionality where y increases 15 times for each unit increase in x.)
c. This is a proportional relationship because the y-intercept is (0,0). (In a proportional relationship, the line always passes through the origin, indicating that when x is zero, y is also zero.)
Thus, the answers are:
a. 15
b. y = 15x
c. (0,0)