question for F3 不知道怎么算出来的？？

At 30 September 20x6, Zenden Limited had an allowance for receivables of $37,000. During the year ended 30 September 20x7 the company wrote off debts totally $18,000, and at the end of the year it is decided that the allowace should be $20,000.

What should be included in the profit and loss account for bad and doubtful debts for the year ended 30 September 20x7?
a. $17,000 Cr
b. $38,000 Dr
c. $1,000 Cr
d. $1,000 Dr



Answer is : d.
please help me to find out how to get this answer

allowance for doubtful debts 在年初和年末分别是37000和20000，你做一个T字账 credit sides37000，debit sides 20000，这样会有一个差额在debit sides17000，这17000要转入bad debts（credit sides）中，题中说今年的坏账一共是18000（debit sides）减去credit sides中的 17000，就剩下1000了（credit sides），这样这1000转入profit&loss acoount中就是在 debit sides上的1000了

哈哈，谢谢，我懂了