108
81
60.75
3 * 2 = 6 * 3= 18 *4 =72 *5 = 360
Based on the sample you have provided, I see that 4 numbers, counting by 2 from 12 to 18, form a repeating sequence. I would expect that the next 4 numbers in this series would again be 12, 14 16, and 18.
The next number in the series 4, 12, 6, 12, 36, 18, 36
The next number in the series 4-12-6-12-36-18-36.. is 108.
18
108
108
24
26
108
108
24
30!
The number 7 comes next.