#### Answer

$43^{\circ}$

#### Work Step by Step

For coin to be illuminated, light beam after refraction on the water should hit the coin in the water.
Now, $tan\theta_{r}=\frac{0.9}{1.5}=\frac{3}{5}$
Which gives us $\theta_{r}=31^{\circ}$
By Snell's law, $n_{a}sin\theta=n_{w}sin\theta_{r}$
Thus, $1\times sin\theta= 1.33\times sin31^{\circ}$
Hence, $\theta = 43^{\circ}$