For each of the following $A.P.s$,find the $n^{th}$ term: $10.5, 11.7, 12.9, 14.1, \dots$

For an $A.P.$,the $3^{rd}$ term is $7$ and the $7^{th}$ term exceeds thrice the $3^{rd}$ term by $2$. Find the sum of first $20$ terms of the $A.P.$

For an $A.P.$,the $12^{th}$ term is $4$ and the $20^{th}$ term is $-20$. Find the $n^{th}$ term of the $A.P.$

Find the sum:
$4-\frac{1}{n}+4-\frac{2}{n}+4-\frac{3}{n}+\ldots$ up to $n$ terms.

In an $AP$ if $a = -7.2, d = 3.6, a_{n} = 7.2,$ then $n$ 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 $d$.