Final answer:
The sum of the numbers in the series is -8208.
Step-by-step explanation:
The sum of a series can be found using the formula for the sum of an arithmetic series, which is given by:
Sum = (n/2)(first term + last term),
where n is the number of terms and the first and last terms are provided in the series. In this case, the first term is 15 and the last term is -129. The common difference between each term is -4.
Using the formula, we have:
Sum = ([-129 - 15]/2)(15 + -129) = (-144/2)(-114) = 72 * -114 = -8208.
Therefore, the sum of the numbers in the series is -8208.