Gavin's unpaid credit card balance is $2103.23. His APR is 14.4%.

What is his new balance if he made one new transaction for $390?

APR stands for Annual Percentage Rate, we need to know this before we proceed with the calculations. Gavin's unpaid balance is $2103.23 and new credit amount is $390. New total credit amount is $2493.23, multiplying this with APR value which is 0.144 plus the total credit amount equals to the total balance. Hence, calculation is shown below:

Total balance = (($2103.23+$390) * 0.144) + ($2103.23+$390) = $2852.255

Gavin needs to pay the total credit balance amounting to $2852.255.