1. The problem statement, all variables and given/known data The problem from Sterway, Jewett book. 3. The attempt at a solution The answer in the book is something like 0,141 nm, as I remembered but I cannot achieve such answer coz' I cannot understand what actually asking, d is looks like a distance between two centers of the atomic spheres, but I don't think that it can be 0,141 nm, probably due to my English language, so can somebody clarify for little bit, what the hell I need to find in this problem. I am stucked for now, and my brain will start to melt soon. And imho - this book have too much of unnecessary problem, 70 problem for the first chapter is too much... Thanx.