Thane Company is interested in establishing the relationship between electricity costs and machine hours. Data have been collected and a regression analysis prepared using Excel. The monthly data and the regression output follow:

Month	Machine Hours	Electricity Costs
January	3,200	$	18,750
February	3,600	$	21,700
March	2,600	$	13,850
April	3,800	$	23,700
May	4,500	$	28,600
June	4,000	$	22,700
July	5,200	$	25,100
August	4,200	$	23,100
September	2,700	$	16,200
October	4,400	$	26,700
November	6,000	$	31,700
December	5,700	$	28,100

Summary Output
Regression Statistics
Multiple R	.924
R Square	.854
Adjusted R2	.840
Standard Error	2,090.15
Observations	12.00

	Coefficients	Standard Error	t Stat	P-value	Lower 95%	Upper 95%
Intercept	4,863.95	2,487.74	1.96	0.08	(679.08)	10,406.98
Machine Hours	4.45	0.58	7.66	0.00	3.15	5.74

If the controller uses regression analysis to estimate costs, the estimate of the variable portion of electricity cost is:

a. Variable Cost = $7.66 Machine-hours.

b. Variable Cost = $0.85 Machine-hours.

c. Variable Cost = $4.45 Machine-hours.

d. Variable Cost = $0.58 Machine-hours.