The school has determined that the following biweekly revenues and costs occur at different levels of enrollment: Number of Students Enrolled Total Revenue Total Costs
10 $3,000 $2,100
15 4,500 2,700
16 4,800 2,800
20 6,000 3,200
21 6,300 3,255

The marginal cost when the twenty-first student enrolls in the school is: