If you’re not afraid of losing, a good way to get out of the wagering requirement is to bet aggressively early, either going for a big win or go bust trying. If you make the big win then grind out required play more conservatively. However, that isn’t what you were asking. The probability of turning $400 into $5,900 ($5,500 in winnings), assuming no house edge, is 400/5,900 = 6.78%. Of course there usually is a house edge but if you’re smart you can keep it very low. So 6.78% would be an upper bound on the probability.