x35, x40, x50 is the roll over needed for bonus to be unlocked in most casinos. If you are lucky you will run into some promotion that has lower roll over, but that rarely happen, in my 5 years in gambling I had just few bonuses with lower roll over.
Is it possible to win it, yes! There are too options, first is to try to play with higher odds and win something big so you can win bonus faster, other is to take it easy and play with the smallest odds and in 10 days to complete the bonus if you can. I am more in favor of the first option, to try harder and in case you win big you can rise your bets and fnish bonus faster!