We start with $1,187.92 With the interest and the late fee charge $1,187.92 (1 + 0.1225/12) + 30 = $1,230.05 With the interest minus the payment of $125 $1,230.05 (1 + 0.1225/12) - $125 = $1,117.60
The new principal after the latest payment is $1,117.60.
