Answer
The speed of light in material 1 is $~~2.0\times 10^8~m/s$
Work Step by Step
From the graph, we can see that the refracted angle is $30^{\circ}$ when $n_2 = 1.50$
Since this angle is the same as the incident angle, the index of refraction of material 1 must also be $n_1 = 1.50$
We can find the speed of light in material 1:
$v = \frac{3.0\times 10^8~m/s}{1.50} = 2.0\times 10^8~m/s$
The speed of light in material 1 is $~~2.0\times 10^8~m/s$
