1. The problem statement, all variables and given/known data Four congruent spheres, radius length 10 cm, are placed on a horizontal table so that each touches two others and their centres form a square. A fifth congruent sphere rests on them. Find the height of the top of this fifth sphere above the table. 2. Relevant equations Not found. 3. The attempt at a solution I have been thinking of this for 2 days, but to be honest, I have no idea have to solve this. I tried the 2D problem, which has 2 congruent circles, and 1 congruent circle on top of the them. This problem seems to be easier and I worked it out. Yet this one is different and I hope I will be given a helping hand. Thank you, everyone.