Laura’s credit card has an apr of 12.04%, and it computes finance charges using the daily balance method and a 30-day billing cycle. on june 1st, laura had a balance of $606.40. she made exactly one transaction in june: a payment of $55.25. if laura’s finance charge for june was $5.71, on which day did she make the payment?

Finance charge is equal to:
daily balance*A*P*R*billing cycle/365
db  0.1204  30/365 = 5.71
db = 577.01 (I am rounding every answer, and keeping the number in my calculator, things won't work out exactly if you calculate using my numbers)Manipulate the formula for mean:
average = total/amount
577.01 = total/30
total over 30 days = 17,310.22Set up an equation with our information:
606.40x + 55.25(30-x) = 17,310.22
551.15x = 16,652.72
x = 28.4

The balance was $606.40 for 28 days, so she paid on the 29th.