(A) 9/4 × 10⁸ m/s
Using $n = c/v$: speed in water $= c/n_w$ and speed in glass $= c/n_g$.
$$\frac{v_w}{v_g} = \frac{n_g}{n_w} = \frac{3/2}{4/3} = \frac{9}{8}$$
$$v_w = \frac{9}{8} \times 2 \times 10^8 = \frac{9}{4} \times 10^8 \text{ m/s}$$
Source: Chapter 9, Section 9.3.2 The Refractive Index
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The key relation is $n = c/v$, so $v = c/n$. Rather than finding $c$ separately, take the ratio of speeds in the two media: $v_w/v_g = n_g/n_w$. This eliminates $c$ and gives the answer directly. Examiners expect you to show the ratio step clearly before substituting the given speed in glass.