Thornton Computer Services, Incorporated, has been in business for six months. The following are basic $$operating data for that period:

Month

July August September October November December

Service hours $120136260420320330$

Revenue $ $6,000$ $ $6,800$ $ $13,000$ $ $21,000$ $ $16,000$ $ $16,500$

Operating costs $ $4,300$ $ $5,300$ $ $7,100$ $ $11,200$ $ $9,100$ $ $10,600$