Problem 5.74

The distances from a Fresnel biprism to a narrow slit and a screen are equal to $a=25 \mathrm{~cm}$ and $b=100 \mathrm{~cm}$ respectively. The refracting angle of the glass biprism is equal to $\theta=20^{\prime}$. Find the wavelength of light if the width of the fringe on the screen is $\Delta x=0.55 \mathrm{~mm}$.