Suppose a series of $n$ terms is given by $\displaystyle S_{n}=a_{1}+a_{2}+...+a_{n}$ Then $\displaystyle S_{n-1}=a_{1}+a_{2}+...+a_{n-1}\left ( \forall \ n > 1 \right )$ and then we can write $\displaystyle t_{n}=S_{n}-S_{n-1} \ \forall n\geq 2$ for $ n=1 $ we have $\displaystyle S_{1}=t_{1}$ On the basis of above information answer the following questions If sum to $ n$ terms of a series is $\displaystyle an^{2}+bn$ where $a$, $b$ are constants then $ 5^{th} $ term of the series is