The cutoff frequency of TE₀₁ mode of an air filled rectangular waveguide having inner dimensions a cm×b cm (a>b) is twice that of the dominant TE₁₀ mode. When the waveguide is operated at a frequency which is 25% higher than the cutoff frequency of the dominant mode, the guide wavelength is found to be 4 cm. The value of b (in cm, correct to two decimal places) is