#### Answer

The first four terms are,${{a}_{1}}=1,{{a}_{2}}=11,{{a}_{3}}=21\text{ and }{{a}_{4}}=31$ and the $8\text{th}$ term is ${{a}_{8}}=71$, and the $12\text{th}$ term is ${{a}_{12}}=111$.

#### Work Step by Step

${{a}_{n}}=10n-9$ …… (1)
To find the value of the first term, ${{a}_{1}}$ put $n=1$ in equation (1)
$\begin{align}
& {{a}_{n}}=10n-9 \\
& {{a}_{1}}=10\cdot 1-9 \\
& =10-9 \\
& =1
\end{align}$
For the second term, ${{a}_{2}}$ put $n=2$ in equation (1)
$\begin{align}
& {{a}_{n}}=10n-9 \\
& {{a}_{2}}=10\cdot 2-9 \\
& =20-9 \\
& =11
\end{align}$
For the third term, ${{a}_{3}}$ put $n=3$ in equation (1)
$\begin{align}
& {{a}_{n}}=10n-9 \\
& {{a}_{3}}=10\cdot 3-9 \\
& =30-9 \\
& =21
\end{align}$
For the fourth term, ${{a}_{4}}$ put $n=4$ in equation (1)
$\begin{align}
& {{a}_{n}}=10n-9 \\
& {{a}_{4}}=10\times 4-9 \\
& =40-9 \\
& =31
\end{align}$
For the $8\text{th}$ term, ${{a}_{8}}$ put $n=8$ in equation (1)
$\begin{align}
& {{a}_{n}}=10n-9 \\
& {{a}_{8}}=10\times 8-9 \\
& =80-9 \\
& =71
\end{align}$
For the $\text{12th}$ term, ${{a}_{12}}$ put $n=12$ in equation (1)
$\begin{align}
& {{a}_{n}}=10n-9 \\
& {{a}_{12}}=10\times 12-9 \\
& =120-9 \\
& =111
\end{align}$