Select the number from among the given options that can replace the question mark (?) in the following series.
24,30,39,51,66,84,?

Let's compute the differences between consecutive terms:
30−24=6

39−30=9

51−39=12

66−51=15

84−66=18

The differences are multiples of 3 increases: 6,9,12,15,18.
Following this arithmetic progression, the next difference must be:

18+3=21
Therefore, the missing number is:

84+21=105