Collapsing Bubble

A conducting bubble of radius $a$ , thickness $t (t<<a)$ has potential $V$ . Now the bubble collapses into a droplet.

The potential of the droplet $V'$ can be given by:

$V' = V {\left ( \frac{a}{mt} \right )}^{\frac{1}{n}}$ , where $m$ and $n$ are integers.

Find the value of $m - 2n$ .