Lana has a credit card that uses the adjusted balance method. For the first 10 days of one of her 30-day billing cycles, her balance was $2800. She then made a payment of $1200, so her balance decreased to $1600, and it remained that amount for the next 10 days. Lana then made a purchase for $500, so her balance for the last 10 days of the billing cycle was $2100. If her credit card's APR is 35%, how much was Lana charged in interest for the billing cycle?