Lowell has a credit card that uses the adjusted balance method. For the first 10 days of one of his 30-day billing cycles, his balance was $1360. He then
made a purchase for $470, so his balance jumped to $1830, and it remained
that amount for the next 10 days. Lowell then made a payment of $740, so
his balance for the last 10 days of the billing cycle was $1090. If his credit
card's APR is 28%, which of these expressions could be used to calculate the
amount Lowell was charged in interest for the billing cycle?