What does the constant of variation mean?

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.)

What adds to be the bottom number but also multiplies to be the top number with 8 on the bottom and 15 on top

Find the dimensions of the circle. area = 64π in.² r= in.