Finding the First n Terms of an Arithmetic Series

Find the sum of each arithmetic series.

1. ⓐ $\text{5}\textrm{ }+\textrm{ }\text{8}\textrm{ }+\textrm{ }\text{11}\textrm{ }+\textrm{ }\text{14}\textrm{ }+\textrm{ }\text{17}\textrm{ }+\textrm{ }\text{20}\textrm{ }+\textrm{ }\text{23}\textrm{ }+\textrm{ }\text{26}\textrm{ }+\textrm{ }\text{29}\textrm{ }+\textrm{ }\text{32}$
2. ⓑ $\text{20}\textrm{ }+\textrm{ }\text{15}\textrm{ }+\textrm{ }\text{10}\textrm{ }+\ldots+\textrm{ }−\text{50}$
3. ⓒ $\sum_{k = 1}^{12} 3 k - 8$