Find the $n^{th}$ term of the $A.P. \, 18, 16.5, 15, 13.5, \ldots$

Ramkali saved ₹ $5$ in the first week of a year and then increased her weekly savings by ₹ $1.75$. If in the $n$-th week,her weekly savings become ₹ $20.75$,find $n$.

The $n^{th}$ term of an $A.P.$ is denoted by:

Find the $100^{th}$ term of the $A.P.$ $50, 56, 62, 68, \ldots$

For a given $A.P.$,the common difference is $5$ and its $15^{th}$ term is $72$. Find the first term of the $A.P.$ and its $50^{th}$ term.

Which term of the $A.P.$ $71, 68, 65, \ldots$ is its first negative term?