Answer
$d=22, a_1=-100.5$
Work Step by Step
With $a_4=-34.5$, the value of $a_5$ can be found by adding the common difference $d$ once.
Since $a_4=-34.5$ and $a_5=-12.5$, then:
\begin{align*}
a_4+d&=a_5\\
-34.5+d&=-12.5\\
d&=-12.5+34.5\\
d&=22
\end{align*}
To find $a_1$, use the formula $a_n=a_1+d(n-1)$ to obtain:
\begin{align*}
a_5&=a_1+22(5-1)\\
-12.5&=a_1+22(4)\\
-12.5&=a_1+88\\
-12.5-88&=a_1\\
-100.5&=a_1
\end{align*}
