Donald, a farmer, deposited \$64,000 in a State Farm Bank deposit scheme for two years and got a simple interest of \$16,000. He withdrew the entire amount after 2 years including interest and deposited in Comercia Bank's saving scheme which offered 2.5% extra interest as compared to State Farm Bank and that too compounded annually. Calculate the total compound interest obtained by Donald after 2 years.

Using the simple interest formula for State Farm Bank, the annual rate equals (16000 / (64000 * 2)) * 100 = 12.5%. The Comercia Bank scheme offers a rate of 12.5% + 2.5% = 15% compounded annually. Donald withdraws his total State Farm amount of $80000 and deposits it into Comercia Bank, so applying the compound interest formula for two years gives the final amount as 80000 * (1.15)^2 = 80000 * 1.3225 = $105800. The total compound interest obtained is $105800 - $80000 = $25800.

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