Which term of the $A.P.$ $-1, 3, 7, 11, \ldots$ is $95$ (in $^{th}$)?

Determine the $AP$ whose fifth term is $19$ and the difference of the eighth term from the thirteenth term is $20$.

The sum of the first $n$ terms of the $A.P.$ $2, 7, 12, 17, \ldots$ is $990$. Find the value of $n$.

The list of numbers $-10, -6, -2, 2, \ldots$ is

For an $A.P.$,the first term is $10$,the $n^{th}$ term is $40$,and the sum of the first $n$ terms is $150$. Find the value of $n$ and the common difference $d$.

The ratio of the $11^{\text{th}}$ term to the $18^{\text{th}}$ term of an $AP$ is $2:3$. Find the ratio of the $5^{\text{th}}$ term to the $21^{\text{st}}$ term,and also the ratio of the sum of the first five terms to the sum of the first $21$ terms.