Expanding the terms, we have:

(3x - 1)(3x + 1) = 9x^2 + 3x - 3x - 1 = 9x^2 - 1

(3x + 1)^2 = (3x + 1)(3x + 1) = 9x^2 + 3x + 3x + 1 = 9x^2 + 6x + 1

Now, adding both expressions together:

(3x - 1)(3x + 1) + (3x + 1)^2 = (9x^2 - 1) + (9x^2 + 6x + 1)
= 9x^2 - 1 + 9x^2 + 6x + 1
= 18x^2 + 6x

Therefore, the final expression is 18x^2 + 6x.