Answer:
3 x 3 x 5
Explanation:
Prime numbers are numbers that cannot factor any lower then itself and one (which includes, but is not limited too: 1, 3, 5, 7, 11, 13, 17, etc.
5 x 1 = 5
3 x 1 = 3
Factor:
45 = 15 x 3
15 = 5 x 3
3 x 3 x 5 is your answer.