you need 30321 * 168,408,013 to solve the a block at current difficulty. so not even close, but not bad at all from a 900gh.

current difficulty according to bitcoinwisdom.com = 5,106,422,924,659 , so your share needs to => than that.

but it changes every aprox 14 days, so you check it on the website from time to time.

good luck.