BPP question on Irrecoverable debts and allowances

11.17) At 1 January 20X4, Tartar Co had total receivables of $380,000. A specific allowance of
$20,000 had
been made for a business customer, Drab. The general allowance for receivables was
2.5%. During the
year, Drab went out of business owing Tartar Co $28,000, none of which is expected to
be recovered.
At 31 December 20X4, Tatar had total receivables of $420,000. There were no specific
allowances but the general allowance for receivables was increased to 3%.
What is the charge in the statement of profit or loss for the year to 31 December for the
allowance for receivables and irrecoverable debts?

A $16,400
B $31,600
C $44,400
D $11,600

I tried this question over and over again but couldn’t get any of these answers.
But when checking the answers on the back of the book:

Specific allowance for receivables at 1 January 20,000
General allowance: 2.5% of (380,000 – 20,000) 9,000
———–
29,000
———–
General allowance at 31 December: 3% of 420,000 12,600
Reduction in allowance for receivables (16,400)
Irrecoverable debt written off 28,000
———-
Combined expense in statement of profit or loss 11,600
———-

According to the answer the irrecoverable debt of 28,000 wasn’t substracted from the total receivables of 420,000 before creating the general allowance. Is the answer correct or should the general allowance be 11,760 and the expense in the SOPL be 10,760.