In a single slit difraction pattern, a light of wavelength 6000$\mathop A\limits^o$ is used. The distance between the first and third minima in the difraction pattern is found to be $3 \mathrm{~mm}$ when the screen in placed $50 \mathrm{~cm}$ away from slits. The width of the slit is _________ $\times 10^{-4} \mathrm{~m}$.