Look at this series: 15, 15, ?, 27, 39, 39, ... What number should fill the blank? Choose the correct choice from the following answers
A) 51 B) 39 C) 27 D) 15 E) None
Explanation: In this simple addition with repetition series, each number in the series repeats itself, and then increases by 12 to arrive at the next number.   Answer: Option 27
<result>C</result>
Look at this series: 15, 15, ?, 27, 39, 39, ... What number should fill the blank?