Insert the missing number.
3, 5, 6,10 , 9, 15, 12, 20, 15, (....)
Options:
A) 25
B) 20
C) 10
D) 30
E) 15
Explanation:   There are two series, beginning respectively with 3 and 5. In one 3 is added and in another 5 is added.   The next number is  20 + 5= 
<gadget id="calculator"> 20 + 5</gadget>
<output>25</output>
25.   25nswer: 25) 25
<result>A</result>
Insert the missing number.
3, 5, 6,10 , 9, 15, 12, 20, 15, (....)