What is the radius R2 of the largest circle that can fit in the space at the centre of the square, bounded by the outer circles?

If 8 spheres of radius R1 are now similarly arrange inside a cube of edge length 4r1, what is the radius r3 of the largest sphere that can fit in the space at the centre of the cube?

What is the radius R2 of the largest circle that can fit in the space at the centre of the square bounded by the outer circles If 8 spheres of radius R1 are now class=