Which number should be in place of the question mark (?) In the following series?1.5, 5, 10.5, ?, 27.5

Which number should be in place of the question mark (?) In the follow

1.	Which number should be in place of the question mark (?) In the following series?1.5, 5, 10.5, ?, 27.5
A.	12
B.	18
C.	11
D.	14
Answer» C. 11