Q29. In Young's double slit experiment, carried out with light of wavelength $5000 \backslash \mathrm { AA }$, the distance between the slits is 0.3 mm and the screen is at 200 cm from the slits. The central maximum is at $x = 0 \mathrm {~cm}$. The value of $x$ for third maxima is $\_\_\_\_$ mm .