Aakash has coins of 50 paise, 25 paise and Rs. 1.50 in the ratio 1 : 2 : 3 (Aakash stays in a country where all are valid currency coins. Also, in his country, 1 rupee = 100 paise). How many coins of 25 paise does Aakash have, if he has got Rs.6,600 in all?