Can any term of the $A.P.$ $3, 7, 11, \ldots$ be $184$?

$A$ class has $49$ students who are allotted roll numbers from $1$ to $49$. Find a roll number $n$ such that the sum of all the roll numbers smaller than $n$ is equal to the sum of all the roll numbers greater than $n$.

The $8^{th}$ term of an $A.P.$ is $31$ and its $15^{th}$ term exceeds its $11^{th}$ term by $16$. Find the $A.P.$ and also its $20^{th}$ term.

If $a=2$ and $d=4,$ then $S_{40}=\ldots \ldots \ldots$

The $10^{th}$ term of an $A.P.$ is $52$ and its $17^{th}$ term exceeds its $13^{th}$ term by $20$. Find the $A.P.$ and also its $30^{th}$ term.

Which of the following form an $AP$? Justify your answer.
$(i)$ $-1, -1, -1, -1, \ldots$
$(ii)$ $0, 2, 0, 2, \ldots$
$(iii)$ $1, 1, 2, 2, 3, 3, \ldots$