Will 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 cots 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 Will Company continue to purchase Part X or begin making it?