Use the formula to evaluate the series 3-9+27-81 + ... - a8

In the given series, we see that the first term is 3 and the common ratio between the succeeding terms is - 3. To solve for the sum of the first 8 terms, we use the equation,

Sum = (a1) (1 - r^n) / (1 - r)

Substituting the known terms,

Sum = (3) (1 - (-3) ^8) / (1 - - 3) = - 4920

Thus, the answer is - 4920.