You decide to take out an ordinary interest loan of $30,000 at 4%, on a 90 day

Question:

You decide to take out an ordinary interest loan of $30,000 at 4%, on a 90 day note.
a) In 45 days you decide to make a payment of $10,000 on the loan. What is your new principal? Explain how you got the answer.
b) How much did you pay at the end of the loan overall?
How does this differ from how much you would have paid overall had you not made a payment of $10,000 after 45 days?