Answer:
y = m λ L / d
must use lasers of greater wavelength
Explanation:
The expression for the constructive interference of a double slit is
      d sin θ = m λ
let's use trigonometry to find the angle
     tan θ = y / L
in interference phenomena the angles are small
     tan θ= sin θ/ cos θ = sin θ
     sin θ = y / L
we subjugate
     d y / L = m λ
     y = m λ L / d
In this expression we see that the separation of the lines (and) increases linearly with the wavelength, therefore we must use lasers of greater wavelength
