$y$ years ago,the sum of the ages of five friends was $x$ years,then the sum of the present ages of them is $\ldots \ldots \ldots \ldots$ years.

The eighth term of an $AP$ is half its second term and the eleventh term exceeds one third of its fourth term by $1$. Find the $15^{\text{th}}$ term.

Find the sum of the first $17$ terms of an $AP$ whose $4^{\text{th}}$ and $9^{\text{th}}$ terms are $-15$ and $-30$ respectively.

If the sum of the first $14$ terms of an $AP$ is $1050$ and its first term is $10,$ find the $20^{th}$ term.

Jaspal Singh repays his total loan of $Rs. 118000$ by paying every month starting with the first instalment of $Rs. 1000$. If he increases the instalment by $Rs. 100$ every month,what amount will be paid by him in the $30^{\text{th}}$ instalment? What amount of loan does he still have to pay after the $30^{\text{th}}$ instalment?

In an $AP$ given $a_{n}=4, d=2, S_{n}=-14$,find $n$ and $a$.