Since having greater refractive index mean light will travel slower, and the speed of the light is inversely proportional to the refractive index of the medium. The speed of light in the first medium is $frac{1.33}{1.20}=1.10$ times more than the second medium.

This is possible if the angle of incidence is 0$text{textdegree}$, then the angle of refraction will also be 0$text{textdegree}$ no matter what is the refractive index of the medium. So when light travelling from a medium having greater refractive index, incident on a medium having lower refractive index, normally at the interface, the speed will increase but direction will not change.

The total time needed for light to travel through ice is
$$
t_1=frac{0.32text{ m}}{v_{ice}} =frac{0.32text{ m}}{frac{c}{n_{ice}}} = frac{n_{ice}times 0.32text{ m}}{c} = frac{1.31times 0.32text{ m}}{3times10^8text{ m/s}} = 1.4text{ ns}
$$

while through water

$$
t_2=frac{4text{ m}-0.32text{ m}}{v_{water}} =frac{3.68text{ m}}{frac{c}{n_{water}}} = frac{n_{water}times 3.68text{ m}}{c} = frac{1.33times 3.68text{ m}}{3times10^8text{ m/s}} = 16.3text{ ns}
$$

yielding for the total time

$$
t=t_1+t_2=17.7text{ ns}.
$$

Using Snell’s law we know that

$$
n_{air}sinalpha_{in}=n_{material}sinalpha_{reff}.
$$

Putting $n_{air} = 1$ we get

$$
n_{material} = frac{sinalpha_{in}}{sinalpha_{reff}} = frac{sin 25^circ}{sin15^circ} = 1.63.
$$

Using Snell’s law we know that

$$
n_{air}sinalpha_{in}=n_{material}sinalpha_{reff}.
$$

Putting $n_{air} = 1$ we get

$$
sinalpha_{ref} = frac{sinalpha_{in}}{n} = frac{sin35^circ}{1.38}Rightarrow alpha_{ref}=arcsinleft( frac{sin35^circ}{1.38}right)=24.5^circ.
$$

a) Since the light is coming from the material with greater refractive index to the material with lower refractive index the angle of incidence is less than the angle of refraction i.e. $42^circ$.

b) Using Snell’s law we have

$$
2.41sinalpha_{in} = 1.33sin 42^circRightarrow sinalpha_{in} = frac{ 1.33sin42^circ}{2.41}Rightarrowalpha_{in} = arcsinleft(frac{1.33sin42^circ}{2.41}right) = 22^circ.
$$