Customer buys 1 of each bulb, therefore subtract 1 from each type of bulb.
Remaining bulbs:
5 amaryllis
6 daffodils
4 lilies
3 tulips
Total number of flowers left in basket = 18 flowers
Next customer buys 1 flower at random. Thus, your odds are equal to number of amaryllis in basket/total number of flowers left in basket.
So, the odds of getting an amaryllis flower in the basket is 5/18.