Two immiscible liquids of refractive indices $\frac{8}{5} and \frac{3}{2} respectively are put in a beaker as shown in the figure. The height of each column is 6 \mathrm{~cm}. A coin is placed at the bottom of the beaker. For near normal vision, the apparent depth of the coin is \frac{\alpha}{4} \mathrm{~cm}. The value of \alpha$ is _________.
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