For this problem, let's use the approach of dimensional analysis. This technique is done by cancelling out like units that appear both on the numerator and the denominator side. As a result, this technique will let you know that your final answer conforms to what parameter is asked. In this case, the final answer should be in $. The solution is as follows:
$560/troy ounce * 1 troy ounce/480 grains * 1 grain/64.8 mg * 1000 mg/1 g * 1 g = $18
