There are two water tanks X andY , X is much smaller than Y. While water fills at the rate of 1 liter every hour in X, it gets filled up like, 10, 20, 40, 80, 160 in tank Y. (At the end of first hour, Y has 10 liters, second hour it has 20 liters and so on). If tank Y is 1/32 filled of the 21 hours, what is total duration of hours required to fill it completely?