Rob quit a job working 15 hours per week at a Subway sandwich shop to make sandwiches in his college dorm room that he sells to hungry students. If he had been paid $8 per hour at Subway and now works the same 15 hours per week but sells his sandwiches for $300 per week and pays only $100 per week for the supplies, how much economic profit does he make?
A. $300 per week
B. $40 per week
C. $80 per week
D. $20 per week