Answer
$V^{-1}$ is used to calculate the number of years after 2008,
after which the stamp will reach a given value.
Work Step by Step
If V(t) assigns (a value) to (the number of years passed),
then $V^{-1}(t)$ assigns (a number of years) to (a given value in dollars).
$V^{-1}(t)$ could be used on a given value of the stamp
to determine how many years since 2008 will pass until the stamp achieves that value.
