On June 1, Green Pea, Inc. purchased $1,200 worth of supplies on account. Prior to the purchase, the balance in the supplies account was $0. On December 31, the fiscal year-end for Green Pea, it is determined that $500 of supplies have been used up. What is the balance in the supplies account after adjustment?

Simply add your balance in the supplies account prior to the purchase and add your purchase amount to get your new supplies account balance. Now just subtract your supplies that have been used to get your ending account balance.