complete series: 3, 4, 7, 8, 11, 12. X. ……?

1. 10
2. 12
3. 14
4. 15
5. None of these

The given sequence is:

3, 4, 7, 8, 11, 12

Form differences between two consecutive numbers in the sequence as follows:

4 – 3 = 1

7 – 4 = 3

8 – 7 = 1

11 – 8 = 3

12 – 11 = 1

X- 12 = 3

= 15