Fill in the blanks: 18,9, () 4.5 3.6

Fill in the blanks: 18,9, () 4.5 3.6

In this way, 18 is one time of 18, two times of 9, three times of (), four times of 4.5 and five times of 3.6, so the one to be filled in is 6, 18 is three times of 6