Chapter 19.4, Problem 41E

To determine

The term with $b^5$ in ${\left(a+b\right)}^8$ where the $r+1$ term of the expansion ${\left(a+b\right)}^n$ is $\frac{n\left(n-1\right)\left(n-2\right)\cdots \left(n-r+1\right)}{r!}{a}^{n-r}{b}^r$.