Lisbon Corporation is analyzing the following costs with respect to its decision to expand production and sales volume:

New delivery equipment cost, $170,000.

Annual depreciation expense on the new delivery equipment, $17,000.

Old delivery equipment cost, $133,000.

Annual depreciation expense on the old delivery equipment, $13,300.

Annual decrease in utilities cost, $1,400.

Annual increase in advertising costs, $6,800.

Annual increase in sales, $81,000.

Annual increase in cost of goods sold, $21,000.

Annual increase in sales commissions, $1,500.

Annual increase in shipping costs, $400.

How much is the differential annual net operating income?

a. $36,500

b. $56,400

c. $49,000

d. $35,700