According to the US Rule, adjusted balance is calculated as:
On the 1st payment:
Adjusted balance = Note initial value + Interest – Payment
On the 2nd payment:
Adjusted balance = Adjusted balance from 1st payment + Interest – Payment
On the 1st payment, her adjusted balance was:
Interest = $5,000 * 0.05 * 40 / 360
Interest =$27.78
Adjusted balance = $5,000 + $27.78 - $500
Adjusted balance = $4,527.78
On the 2nd payment, her adjusted balance was:
Interest = $4,527.78 * 0.05 * (90 – 40) / 360
Interest = $31.44
Adjusted balance = $4,527.78 + $31.44 - $500
Adjusted balance = $4,059.22 (ANSWER)