Olby and sarah sold newspapers this past summer. colby earned $4.50 for each newspaper he sold. sarah's earnings were $35 less than colby's at the end of the summer. the following expression shows sarah's earnings:

4.50y − 35

in the expression, what does the variable y represent?

sarah's earnings at the end of the summer
colby's earnings at the end of the summer
the number of newspapers that sarah sold
the number of newspapers that colby sold