Answer
a) ${{a}_{n}}=0.3n+24.1$.
b) $33.1\%$
Work Step by Step
(a)
The general equation of the nth term is given by ${{a}_{n}}={{a}_{1}}+\left( n-1 \right)d $.
So, $\begin{align}
& {{a}_{n}}={{a}_{1}}+\left( n-1 \right)d \\
& {{a}_{n}}=24.4+\left( n-1 \right)0.3 \\
& {{a}_{n}}=24.4+0.3n-0.3 \\
& {{a}_{n}}=0.3n+24.1 \\
\end{align}$
(b)
We use $ n=30$ because after 1989 until 2019, 30 years pass.
So, $\begin{align}
& {{a}_{n}}=0.3n+24.1 \\
& {{a}_{n}}=0.3\left( 30 \right)+24.1 \\
& {{a}_{n}}=33.1 \\
\end{align}$
