Twisty Pretzel Company produces bags of pretzels that are sold in cases and retailed throughout the United States. Its normal selling price is $30 per case; each case contains 15 bags of pretzels. The variable costs are $19 per case. Fixed costs are $25,000 for a normal production run of 5,000 cases per month. Twisty Pretzel received a special order from an existing customer which it could accommodate without exceeding capacity. The order was for 1,500 units at a special price of $20 per case; a variable selling cost of $1 per case included in the variable costs would not be relevant for this order. If the order is accepted, the impact on operating income would be a(n) ________.

decrease of $750

decrease of $4,500

increase of $1,500

increase of $3,000