Answer:
The length of the side of the hole in the second cardboard sheet is 
Explanation:
From the question we are told that
The distance of the point source from the screen is 
The length of a side of the first square hole is 
The distance of the cardboard from the point source is 
The distance of the second cardboard from the point source is 
Let take the
as the angle at which the light is passing through the edges of the cardboards square hole
Since the bright square casted on the screen by both square holes on the individual cardboards are then it means that

This implies that
Looking at this from the SOHCAHTOA concept
Here opposite is the length of the side of the first cardboard square hole
and
Adjacent is the distance of the from the first cardboard square hole to the point source
And for
Here opposite is the length of the side of the second cardboards square hole (let denote it with
)
and
Adjacent is the distance of the from the second cardboards square hole to the point source
So

And
Substituting this into the above equation

Making
the subject


Since it is a square hole the sides are the same hence
The length of the side of the hole in the second cardboard sheet is 