Answer:
First one is wrong. x should be 16.
Second one is not completely visible, so cannot say.
Step-by-step explanation:
In the last step, the divison by 4 yields:
x/16 = 1, so x = 16
Explanation:
To achive that you have to piant a ring in red, which will have its big diameter equal to the sphere diameter and its small diameter equal to the cube diagonal.
The diagonal of the cube can be calculated using Pithagoras:

Where D is the diagonal and L is the side of the cube
1/3 has the greatest value