Climate-Control, Inc., manufactures a variety of heating and air-conditioning units. The company is currently manufacturing all of its own component parts. An outside supplier has offered to sell a thermostat to Climate-Control for $20 per unit. To evaluate this offer, Climate-Control, Inc., has gathered the following information relating to its own cost of producing the thermostat internally:

		Per Unit		15,000 Units per year
Direct materials	$	6	$	90,000
Direct labor		8		120,000
Variable manufacturing overhead		1		15,000
Fixed manufacturing overhead, traceable		5*		75,000
Fixed manufacturing overhead, common, but allocated		10		150,000
Total cost	$	30	$	450,000

*40% supervisory salaries; 60% depreciation of special equipment (no resale value).

	Per Unit
	Differential
	Costs		15,000 Units
	Make	Buy	Make	Buy
Cost of purchasing		$20		$300,000
Direct materials	6		90,000
Direct labor	8		120,000
Variable manufacturing overhead	1		15,000
Fixed manufacturing overhead, traceable	2		30,000
Fixed manufacturing overhead, common	0	0	0	0
Total costs	$17	$20	$255,000	$300,000
Difference in favor of making (buying)	$3		$45,000

Can someone please explain what I bolded???? I don't understand at all!!