Heather owns a remedial math lesson franchise. Her math lessons are priced at a standard price of $50 an hour per student. She employs five (5) math teachers who tutor ten (10) students per hour. Her math teachers earn $40 an hour. She is considering hiring an additional math teacher so that she would have six (6) employees and could tutor twelve (12) students an hour. What would the Marginal Revenue of the 6th worker be?