Ethan bought 3 pints of raspberries for $5 per pint and x pints of blueberries for $3 per pint. The average cost of all the berries he bought was 15+3x/3+x dollars per pint. If the equation y= 15+3x/3+x is graphed in the xy-plane,what quantity will be represented by the y-intercepy of the graph?