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What aspects of lines have to be diffrent

Arestaurant offers a $12 dinner special that has 5 choices for an appetizer, 12 choices for an entrée, and 4 choices for a dessert. how many different meals are available when you select an appetizer, an entrée, and a dessert? a meal can be chosen in nothing ways. (type a whole number.)

Solve the following pair of equations for x and y: ax/b_ by /a= a +b; ax - by = 2ab