6.66666667 should be your answer...probably should round it though
Cost per ounce means you take the cost and divide it by the cost:
<span>3.36 / (21/2) </span>
<span>division of fractions changes to the multiplication of the reciprocal: </span>
<span>3.36 * (2 / 21) </span>
<span>3.36 and has 21 as a factor, so let's cancel it: </span>
<span>0.16 * 2 </span>
<span>$0.32 per ounce</span>
