The table given below shows the total revenue and total cost of producing a commodity. Table 9.1 Total Output Total Revenue Total Cost $0 $1,000 $1,700 $2,000 $3,300 $2,800 3 $4,800 $3,500 $6,200 $4,000 $7,500 $4,500 $8,700 $5,200 $9,800 $6,000 $10,800 $7,000 $11,700 $9,000 In Table 9.1, the marginal cost of producing the sixth unit of output is equal to