If n^th term of an A.P. is 6n - 15, then its common difference is :

1. 6

2. -6

3. 12

4. -12

Given,

⇒ a_n = 6n - 15

∴ a_{n - 1} = 6(n - 1) - 15 = 6n - 6 - 15 = 6n - 21.

Common difference = a_n - a_{n - 1}

= 6n - 15 - (6n - 21)

= 6n - 6n - 15 + 21

= 6.

Hence, Option 1 is the correct option.