The given sequence is an arithmetic progression with first term a = 5 and common difference d = 11 - 5 = 6. The sum of the first n terms of an arithmetic progression with first term a and common difference d is given by the formula:

S\(_n\) = n/2(2a + (n-1)d)

Substituting the values for a and d, we get:

S\(_n\) = n/2(2 x 5 + (n-1)6)

= n/2(10 + 6n - 6)

= n/2(6n + 4)

= n(3n + 2)

So, the sum of the first n terms of the given arithmetic progression is n(3n + 2).

Therefore, the correct answer is n(3n + 2)