#### Answer

$2m-16n$

#### Work Step by Step

Using the Distributive Property and then combining like terms, the given expression, $
8m-n-3(2m+5n)
,$ simplifies to
\begin{array}{l}\require{cancel}
8m-n-6m-15n
\\\\=
(8m-6m)+(-n-15n)
\\\\=
2m-16n
.\end{array}