It isn't 9/46 on the river unless you miss on the turn, so you have to multiply 9/46 by the probability that you miss on the turn which is 38/47. When you hit on both, you don't want to count that twice. So 9/47 + (38/47)(9/46) = 35%. Or you can take 1 minus the probability of not making it which is 1 - (38/47)(37/46) = 35%.
You can do all the problems this way, or you can use
www.twodimes.net/poker which does hold'em and omaha.