What is the sum of the first 17 terms of an arithmetic progression if the first term is -20 and last term is 28?

Answer: Option A

First term of AP = a = -20 and last term = l = 28
Number of terms = n = 17
$$\begin{array}{rl}& \text{Sum of AP}=\frac{\text{n}}{2}\left(\text{a}+\text{l}\right)\\ & =\frac{17}{2}\left(-20+28\right)\\ & =17\times 4\\ & =68\end{array}$$