Shift in Central Maxima

As shown in the figure, in Young's double slit experiment, a thin plate of thickness t=10µm and refractive index µ=1.2 is inserted infront of slit S1. The experiment is conducted in air (µ=1) and uses a monochromatic light of wavelength λ=500‌nm. Due to the insertion of the plate, central maxima is shifted by a distance of xβ0. β0 is the fringe-width before the insertion of the plate. The value of the x is ______.