An ice cube has a bubble inside. When viewed from one side the...

Let's assume that the original position of the bubble is $x$ from one side of the ice cube of side $a$.

When the bubble is seen from one side, it can be written that

$\dfrac{x}{\mu} = 12 . . . \left(1\right)$

For the view from the other side, it can be written that

$\dfrac{a - x}{\mu} = 4 . . . \left(2\right)$

From equations (1) and (2), it is given that

$\begin{cases}24 - 12\mu & = & 4\mu \\ & ⇒ & \mu = \dfrac{24}{16} \\ & = & 1 . 5\end{cases}$