Remember that he /she says "simple interest rate of 8.25%"
$500, 000 - $200,000 = $300,000 Simple interest that must be earned.
$200,000 x 0.0825 = $16,500 simple interest earned per year.
$300,000 / $16,500 = 18.18 years for $200,000 to become $500,000.