Marc Company assembles products from a group of interconnecting parts. The company produces some of the parts and buys some from outside vendors. The vendor for Part X has just increased its price by 35 percent, to $10 per unit for the first 5,000 units and $9 per additional unit ordered each year. The company uses 7,500 units of Part X each year. Unit costs if the company makes the part are as follows:

Direct materials..................$3.50

Direct labor................... 2.00

Variable overhead................. 4.00

Variable selling costs for the assembled product .... 3.75

Should Marc continue to purchase Part X or begin making it?