Determination of adjusting entry for Supplies used:
In the given case it is given those Supplies on hand were $ 1,000 at the start of the year. At the end of the year, it was determined that $ 450 of supplies had been used. It means the adjustment is needed to make for the amount of supplies used $450.
The adjusting entry for Supplies used shall be as follows:
Supplies Expense Debit $450
Supplies Credit $450
(Being adjustment made for Supplies used)
Hence the correct answer is:
b. Debit supplies expense, $ 450; credit supplies, $ 450