Insert the missing number.
3, 6, 6, 12, 9, 18, 12, 24, 15, (....)	Choose the correct answer
A) 30  B) 36  C) 42  D) 40  E) 38
Explanation:   There are two series, beginning respectively with 3 and 6. In one 3 is added and in another 6 is added.   The next number is  24+ 6= 
<gadget id="calculator"> 24+ 6</gadget>
<output>30</output>
30.   30nswer: 30) 30
<result>A</result>
Insert the missing number.
3, 6, 6, 12, 9, 18, 12, 24, 15, (....)