Precalculus (6th Edition) Blitzer

a) ${{a}_{n}}=0.3n+24.1$. b) $33.1\%$
(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}