At a certain food stand, the price of each apple is ￠ 40 and the price of each orange is ￠ 60. Mary selects a total of 10 apples and oranges from the food stand, and the average (arithmetic mean) price of the 10 pieces of fruit is ￠ 56. How many oranges must Mary put back so that the average price of the pieces of fruit that she keeps is 52￠?