Prisha deposited $$20,000$ into a fund at the beginning of every quarter for $10$ years. He then stopped making deposits into the fund and allowed the investment to grow for $6$ more years. The fund was growing at $5\mathrm{.}86\%$ compounded monthly. a$.$ What was the accumulated value of the fund at the end of year $10?$ b$.$ What was the accumulated value of the fund at the end of year $16?$ c$.$ What is the total amount of interest earned over the $16-$year period?