I'm sorry. I should have guessed from your first assertation that geometry was beyond your ken. Here are the centers of the four balls in a coordinate system centered on the center of the corner ball. You can confirm that every pair of balls is touching by confirming that
(x1x2)^{2} + (y1y2)^{2} + (z1z2)^{2}
is 100 for each of the six pairs. The first three centers are on the plane z=0, the fourth is above that plane by 8.164996.
(0, 0, 0)
(0, 10, 0)
(8.660254, 5, 0)
(2.886751, 5, 8.164996)
If you still don't understand, someone else will need to respond. This as elementary and obvious as I know how to make it.
