Problem 4 (Required, 25 marks) Mrs. B opens a fund account and deposits some money into the account at the beginning of each month for 3n months. The first deposit is made today. You are given that The amount of each deposit is X in the first 2n months. Starting from the beginning of (2n + 1)th month, the amount of each deposit is increased by $20 every month. The amount value of the account is $8280.2 at the end of nth months The amount value of the account is $18764.37 at the end of (2n)th months. The fund earns interest at a monthly effective interest rate 1.7%. Question: Find the total amount of interest earned from the beginning of (n + 1)th month to the end of (3n)th month