Assuming that Naomi has 18 lillies totally, (including those that haven't bloomed):
Yesterday 1/2 * 18 = 9 bloomed.
That leaves 18 - 9 = 9 not yet bloomed yesterday.
Of those 9, 2/3 of them bloomed today.
so 2/3 * 9 = 6 bloomed today.
9 + 6 = 15 have bloomed in total then.
18 - 15 = 3
3 lilies have not bloomed yet.