A uniform plank

$8$

$.$

$0$

$0$

$$m in length with mass

$5$

$5$

$.$

$0$

$$kg is supported at two points located

$1$

$.$

$0$

$0$

$$m and

$5$

$.$

$0$

$0$

$$m

$,$

$$respectively$,$ from the left

$-$

hand end. What is the maximum additional mass you could place on the right

$-$

hand end of the plank and have the plank still be at rest?