A 580 nm light beam source is used for a double-slit experiment. The slits have a separation of 0.35 mm, while the screen is located 1.6 m from the slits. The central maximum is located at the origin point of the coordinate system. One of the slits is covered with a thin sheet of transparent polythene material. Light will travel slower through this material medium compared to air; therefore, the waves passing through the polythene will be slowed down by 4.5 × 10^-16 s relative to the other slit. Express the value of this delay as a percentage of the wave's period.