Answer:
Y = 17.75 x 10⁻³ m = 17.75 mm
Step-by-step explanation:
Using Young's Double Slit formula below:

where,
Y = fringe separation = ?
λ = wavelength = 568 nm = 5.68 x 10⁻⁷ m
L = distance between slits and screen = 3.5 m
d = slit separation = 0.112 mm = 1.12 x 10⁻⁴ m
Therefore,

Y = 17.75 x 10⁻³ m = 17.75 mm