How does the opportunity cost of a government purchase vary depending on whether the market for the purchased good is perfectly competitive or monopolistic

Wallace company provides the following data for next year: month budgeted sales january $120,000 february 108,000 march 140,000 april 147,000 the gross profit rate is 35% of sales. inventory at the end of december is $29,600 and target ending inventory levels are 10% of next month's sales, stated at cost. what is the amount of purchases budgeted for january?