Walter and the Salad Fixings

Walter Sells a Lot of Salad Fixings lettece

Monday, the produce manager, Walter, stacked the salad display case with 80 heads of lettuce. By the end of the day, some of the lettuce had been sold.

On Tuesday, he checked the display case and counted the number of heads that were left. He decided to add an equal number of heads. (He doubled the leftovers.)

By the end of the day, he had sold the same number of heads as Monday.

On Wednesday, he decided to triple the number of heads that he had left. He sold the same number that day, too.

At the end of this day there were no heads of lettuce left. How many were sold each day?