Answer
$s=2.4$
Work Step by Step
We can write the given statement as a relation:
$s\:\propto\:\frac{1}{r}$
Let's introdue a proportionality constant $\:k\:$ to turn the relation into an equation as:
$s=k\cdot \frac{1}{r}$
We can find the value of $\:k\:$ when we are given $\:r=6\:$ and $\:s=4.$
$4=k\cdot \frac{1}{6}$
$\Rightarrow\: k=24$
So, now our general equation $\:s=k\cdot \frac{1}{r}\:$ becomes:
$s=\frac{24}{r}$
When $\:v=10,\:$ we have:
$s=\frac{24}{10}$
$\Rightarrow\: s=2.4$
