Matt Is Offered a Job Driving the Campus Shuttle Bus

Matt is offered a job driving the campus shuttle bus from 4 P.M.to 6 P.M.each Monday.His reservation wage for this job is $7/hour.
If the campus transportation director offers Matt $50/hour,how much economic surplus will he enjoy as a result of accepting the job?

A) $36
B) $43
C) $50
D) $86