Armer Company is accumulating data to use in preparing its annual profit plan for the coming year. The cost behavior pattern of the maintenance costs must be determined. The accounting staff has suggested the use of linear regression to derive an equation for maintenance hours and costs. Data regarding the maintenance hours and costs for the last year and the results of the regression analysis follow:

Month	Maintenance Cost			Machine Hours
Jan.	$	5,100			840
Feb.		3,900			680
Mar.		4,500			760
Apr.		3,720			660
May		5,250			860
June		3,860			670
July		3,930			680
Aug.		5,370			980
Sept.		5,160			850
Oct.		4,950			830
Nov.		4,200			710
Dec.		4,060			700
Sum	$	54,000			9,220
Average	$	4,500		$	768
Average cost per hour				$	6.00
a (intercept)				$	56.74
b (coefficient)					5.9307
Standard error of the estimate					171.887
R-squared					0.93135
t-value for b					11.6480

At 400 hours of activity, Armer management can be approximately two-thirds confident that the maintenance costs will be in the range of

a) $1,921.20 to $2,709.88.

b) $1,922.11 to $2,708.94.

c) $2,094.31 to $2,536.89.

d) $2,143.65 to $2,487.43.

e) None of these answer choices are correct.