Your grandfather started his own business 65 years ago. He opened a savings account at the end of his sixth month of business and contributed $x. Every six months since then he faithfully saved another $x. His savings account has paid an average interest rate of 5 percent, compounded semi-annually. Today, his account is valued at $304,384.88. How much did your grandfather save every six months?

$500

$320

$400

$250

$480