IRRECOVERABLE DETS AND ALLOWANCES

Hello
Could you please advise how you woud answer the below question?

In the year ended 30 September 20×8, Smith had sales of $7,000,000. Year end receivable amounted to 5% of annual sales. Smith wishes to maintain the allowance for receivables at 4% of receivables and as a result discovers that the allowance is 20% higher tahn a the previous year end.

During the year irrecoverable debts amounting to $3,200 were written off and debts amounting to $450 and previously written off were recovered.

What is the irrecoverable debts expense for the year.

The answer on the book is $5,033 as per below

Year end receivables 5% 7,000,0000 350000
Year end allowance for receivable 4% of 350,0000 14000
Allowance at start of year 100/120 *14000 11667

Increase in allowance 2333

Irrecoverable debts

Write off 3200
Increase in allowance 2333
Less Recov of irrec debts 450

= 5083

My concern is: Why did the calculate the allowance of 4% on 350.000 and not on 350,000-3200 (irrecoverable debt) + 450 (debts previously written off and then paid) 347250?

Thanks

Gabbi