Dana Corp. uses linear regression to estimate costs. The machine hours and related costs for the last year, as well as the regression analysis results, are as follows: Machine Hours 580 420 500 400 600 410 Maintenance Month Cost Jan. $ 4,450 Feb. 3,250 Mar. 3,850 Apr. 3,070 May 4,600 June 3,210 July 3,280 Aug. 4,720 Sept. 4,510 Oct. 4,300 3,550 3,410 Sum $46,200 Average $ 3,850 Average cost per hour a (intercept) b coefficient) Standard error of the estimate R-squared t-value for b 420 620 590 570 450 440 NOV. Dec. 6,000 $ 500 $ 8.00 S205.82 7.2884 34.469 0.99724 60.1050 If machine hours are 400, Aaron's manager can be approximately two-thirds confident that the range of the maintenance costs will be