<p>At a used book store, the owner has priced the books such that the store will earn the same amount of profit on each book it sells. The following graph represents the proportional relationship between the number of books sold (`x`) and the profit made from selling those books (`y` dollars). </p> <linegraph data-props='{"options":{"x_min":0,"y_min":0,"y_max":40,"x_max":32,"cell_size":35,"x_interval":4,"y_interval":5,"x_label":"Number of Books","y_label":"Profit (dollars)","title":"Book Store Profit","x_axis_name":"x","y_axis_name":"y"},"points":[{"id":0,"x":0,"y":0,"show_point":false,"highlight_point":false,"show_coordinates":false,"show_x_intercept":false,"show_y_intercept":false,"x_coordinate_highlight":false,"y_coordinate_highlight":false,"show_x_intercept_point":false,"show_y_intercept_point":false},{"id":1,"x":4,"y":5,"show_point":false,"highlight_point":false,"highlight_point_color":"#A3A3B3","show_coordinates":false,"x_coordinate_highlight":false,"y_coordinate_highlight":false,"show_x_intercept_point":false,"show_y_intercept_point":false,"show_x_intercept":false,"show_y_intercept":false},{"id":2,"x":32,"y":40,"show_point":false,"highlight_point":false,"highlight_point_color":"#A3A3B3","show_coordinates":false,"x_coordinate_highlight":false,"y_coordinate_highlight":false,"show_x_intercept_point":false,"show_y_intercept_point":false,"show_x_intercept":false,"show_y_intercept":false}],"line_segments":[{"first_point_id":0,"second_point_id":2,"show_start_arrow":false,"show_end_arrow":true,"highlight_line":"#A3A3B3"}]}'></linegraph> <p>What is the constant of proportionality for this relationship, as shown in the graph?</br><highlight data-color="#666" data-style="italic">Write your answer as an exact decimal or simplified fraction.</highlight></p>