Sasha noticed that the graph of the sales of yearbooks represented a proportional relationship. How could she have calculated the constant of proportionality by looking at the graph?

In a proportional relationship, the equation is y = kx, where k is the constant of proportionality. Solving for k gives k = y ÷ x, so Sasha could divide any y-value by its corresponding x-value. This is choice A, “divide any y-value by its corresponding x-value.”

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