21. [Provision for bad debts] Nucor [NUE], a large U.S. steel producer, reported the following (amounts in $millions): Years Ended December 31 1997 1998 1999 2000 Allowance for Doubtful Accounts Opening balance $14.6 $18.0 $16.3 $21.1 Charged to earnings 4.2 (1.4) 5.3 Write-offs (net of recoveries) (0.8) (0.3) (0.5) Closing balance $18.0 $16.3 $21.1 $27.6 Other Financial Data Accounts receivable (net) $386.4 $299.2 $393.8 $350.2 Sales 4.184.5 4,151.2 4,009.3 4,586.1 Pretax income 460.2 415.3 379.2 478.3

a. Compute the following ratios (in %): (i) Ending balance of reserves to gross receivables for all years (ii) Accounts written off to revenues for 1997 to 1999

b. Assuming that Nucor had expensed accounts written off rather than accruing a reserve for bad debts, compute pretax income for 1997 through 2000.