A Plastic Cube Is Immersed in Water Having an Index $1.33$

A plastic cube is immersed in water having an index of refraction of $1.33$ . A laser beam in the plastic strikes the interface at an angle of $14.5 ^ { \circ }$ with the normal in the plastic. In the water, this beam makes an angle of $21.8 ^ { \circ }$ with the normal. What is the speed of light in the plastic cube? $\left( c = 3.0 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s } \right)$