Answer:
Step-by-step explanation:
On December 31, 2015
The adjusting entry is shown below:
 Supplies expense A/c Dr $1,200
 To supplies A/c $1,200
(Being supplies account is adjusted) 
The supplies expense is computed by 
= Supplies opening balance + purchase of supplies - supplies on hand at the closing date
= $200 + $1,500 - $500
= $1,200