He buys them at a unit price of 0.80 a CD. (to find this just divide the number of materials by the cost) And he sells them for 0.60 a piece. Then, you have to divide 100 by 0.60, which would be estimated to around 167. ( the exact number is 166.6666667) So, about 167 CD's would have to be sold by him to make at least a profit of $100.
Hope this helped.
