The sum of a series whose nth term is 3(2x+1) can be calculated using the formula: S = (n/2)(3a + 3d + a), where a = the first term of the series and d = the common difference between the terms. In the given series, the first term is 3(2x+1), and the common difference is 3. Therefore, the sum of the series is: S = (n/2)(3(2x+1) + 3(3) + (2x+1)) = (n/2)(9x + 10)