The total cost of a number of items may be calculated when the unit cost is known
and the quantity that will be purchased is decided. For example, if a caterer will
serve a meal for $6.25 per person and 100 people will be served, the total cost
will be $6.25*100 or $625.

You may also need to calculate total cost based on unit cost and number of items
when you are ordering several items of the same kind.