To solve this problem we apply the concepts related to the concept of destructive interference. For the destructive interference for a single slit path difference is,

Where,
D = Slit width
n = Order of the minima
= Angle relative to the original direction of the light
= Wavelength of the light
Now the first minima will have a n=1 then

And the 5 order fringe will have n=5 then

The ratio between the two variables will be



Therefore the slit separation is five times the slit width d=5D