Suppose you want to make a certain kind of tropical punch using bananas, oranges, and papayas. This is what you know.
You know the recipe takes seven pieces of fruit.
You don't know how many of each to put in the punch, but you know that
there are twice as many oranges as bananas.
You know that the seven pieces of fruit cost $5.25, where bananas cost $.50
each, oranges cost $.75 each, and papayas cost $1.25 each.
How many pieces of each type of fruit do you need to make the tropical punch?