For a given $A.P.$,$S_{20} = 100$ and $d = -2$. Then,$a = \ldots$

The first term of an $A.P.$ is $a$ and its common difference is $d$. Then,the $18^{th}$ term of the $A.P.$ is..........

In an $AP$,if $S_{n} = n(4n + 1)$,find the $AP$.

Find the $12^{\text{th}}$ term from the end of the $AP: -2, -4, -6, \ldots, -100$.

The first term of a finite $A.P.$ is $5$ and its last term is $95$. If the common difference of the $A.P.$ is $5$,then there are $\ldots \ldots \ldots$ terms in the $A.P.$

The $7^{th}$ term of an $A.P.$ is $108$ and the $11^{th}$ term is $212$. Then,its $n^{th}$ term is $\ldots \ldots \ldots \ldots$