What is the next number in the sequence : 15,21,24,30,33,39,51,57__?
Choose the correct choice from the following choices:
A) 69 B) 71 C) 67 D) 65 E) 79
next no. = previous + (sum of digits)   15 + (1+5)= 
<gadget id="calculator">15 + (1+5)</gadget>
<output>21</output>
21   21 + (2+1)= 
<gadget id="calculator">21 + (2+1)</gadget>
<output>24</output>
24   24 + (2+4)= 
<gadget id="calculator">24 + (2+4)</gadget>
<output>30</output>
30   30 + (3+0)= 
<gadget id="calculator">30 + (3+0)</gadget>
<output>33</output>
33   33 + (3+3)= 
<gadget id="calculator">33 + (3+3)</gadget>
<output>39</output>
39   39 + (3+9)= 
<gadget id="calculator">39 + (3+9)</gadget>
<output>51</output>
51   51 +(5+1)= 
<gadget id="calculator">51 +(5+1)</gadget>
<output>57</output>
57   57 + (5+7)= 
<gadget id="calculator">57 + (5+7)</gadget>
<output>69</output>
69   69NSWER:69
<result>A</result>
What is the next number in the sequence : 15,21,24,30,33,39,51,57__?