The Willsey Merchandise Company has budgeted $40,000 in sales for the month of December. The company's cost of goods sold is 30% of sales. If the company has budgeted to purchase $18,000 in merchandise during December, then the budgeted change in inventory levels over the month of December is:
a) $4,000 decrease
b) $4,000 increase
c) $2,000 increase
d) $2,000 decrease