The sum of the first $n$ terms of an $A.P.$ is given by $S_{n} = 3n^{2} + 5n$. Find the $n^{th}$ term of the $A.P.$

The $n^{th}$ term of an $A.P.$ is given by $T_n = 4n + 3$. Find the sum of the first $60$ terms of the $A.P.$

Find the sum of first $n$ terms of the $A.P.$ $6, 2, -2, \ldots$

Find the sum:
$1+(-2)+(-5)+(-8)+\ldots+(-236)$

Find the sum of the first $40$ positive integers divisible by $6$.

In a school,students thought of planting trees in and around the school to reduce air pollution. It was decided that the number of trees,that each section of each class will plant,will be the same as the class,in which they are studying,e.g.,a section of Class $I$ will plant $1$ tree,a section of Class $II$ will plant $2$ trees and so on till Class $XII$. There are three sections of each class. How many trees will be planted by the students?