How can a business protect against uncollectible accounts?

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this is a long one!!
for a business that makes advance provisions for uncollectible receivables:
A) Journalize the entries to record the following:

1) record the adjusting entry at 12/31, the end of the fiscal year to provide for doubtful accounts. The accounts receivable account has a balance of 700,000 and the contra asset account before adjsutment has a debit balance of 1,000. Analysis of the receivables indicate doubtful accounts of 21,000
2) in march the following fiscal year the 750$ owed by the Lee Co. on account was written off as uncollectible.
3) 8 months later, 350$ of the Lee Co. is reinstated and payment of the amount was received.
4) in October $300 is received on the $500 owed by the Maxi Co. and the remainder is written off as collectible

B) based on the data in A) (1) above what is the net realizable value of the accounts receivable as reported on the balance sheet as of 12/31

C) assuming that the business had been following the direct write off procedure in accounting for uncollectible receivables, journalize the entries to record the following:
(1) recorded write-off of account of Lee Co. {(a) (2) above}

(2)reinstated account of Lee Co. for $350 and recorded payment of that amount received {(a) (3) above}
(3) recorded the receipt of $300 from Maxi Co. in (a) (4) above and wrote off the remainder owed as uncollectible.
I have worked on this for the last few night and I have so many eraser marks I do not know what is the right answere compared to the mistakes I have made with my eraser marks.