Providing for doubtful accounts

At the end of the current year, the accounts receivable account has a debit balance of $$807,000$ and sales for the year total $$9,150,000.$

a$.$ The allowance account before adjustment has a debit balance of $$10,900.$ Bad debt expense is estimated at $\frac{1}{4}$ of $1\%$ of sales.

c$.$ The allowance account before adjustment has a credit balance of $$8,000.$ Bad debt expense is estimated at $\frac{1}{2}$ of $1\%$ of sales.

Determine the amount of the adjusting entry to provide for doubtful accounts under each of the assumptions $($a through d$)$ listed above.

a$.$ $

b$.$ $$45,800$

c$.$ $

d$.$ $$58,400$