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## Example: Printing an Invoice (CRC Cards)

- The invoice also needs to compute the total amount due.
- To obtain that amount, it must ask each item about the total price.
- Each item must ask the product for the unit price and multiply it by the quantity.

  > Product
  > get description |
  > get unit price |

  > Item
  > print the item | `Product`
  > get total price |

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