Let's find the ratio of thickness of polystyrene and flint glass that would contain the same number of wavelengths of light.
The relation of wavelength for any given medium is:

Where:
λn is the wavelength of the wave medium.
λ is the wavelength in vacuum.
n is the refractive index of the medium.
Now, for the thickness, we have:

dp is the thickness of of polystyrene
df is the thickness of flint glass.
λp is the wavelength of light in polystyrene.
λf is the wavelength of light in flint glass.
Substitute λ/np for λp and λ/nf for λf:

Where:
nf is the refractive index of flint glass = 1.66
n is the refractive index of polystyrene = 1.49
Thus, we have:

Therefore the ratio of thicknesses of polystyrene and flint glass that would contain the same number of wavelengths of light is 1.114
ANSWER:
1.114