6 Petals

Flowers with 6 petals will have 6 flower parts.  These are monocots which have flower parts in multiples of 3.  Some plants that normally produce flowers with 6 petals may incidentally produce a flower with 5 petals and vice versa (the lucky 4-leaf clover, if you will).  To make a proper distinction, try to find other flowers on the same plant or other plants of the same species to determine what is the most common petal number.