Mark Quit His Job as a Salesman Where He Made

Mark quit his job as a salesman where he made $43,000 per year to start his own t-shirt making business.His business expenses are $6,000 per year on rent,$12,000 per year on supplies,and $4,000 per year on part-time help.As for his personal expenses,his apartment costs him $4,800 per year and his personal bills are an extra $1,200 per year.What is Mark's opportunity cost of running the business?

A) $43,000
B) $57,000
C) $65,000
D) $71,000