1.6: An arithmetic series and its sums

An arithmetic series $\displaystyle A$ has first term $\displaystyle a$ and common difference $\displaystyle d$. The sum $\displaystyle S_n$ of the first $\displaystyle n$ terms of $\displaystyle A$ is given by

(a) Find the value of $\displaystyle a$ and the value of $\displaystyle d$.

(b) Find the 20th term of $\displaystyle A$.

Given that

(c) find the value of $\displaystyle p$.