Francisco sold 9 rolls of wrapping paper for a band fundraiser earning the band $22.50. Sharon sold 16 rolls of wrapping paper and earned $40.00 for the band. If this relationship is graphed with the number of rolls sold on the x-axis and the money earned on the y-axis, what is the slope of the graph in dollars per roll?

A. 1.25
B. 2.50
C. 3.75
D. 5.00