I am sorry not to see this till now
It is very much a counting problem where in you can count from top and the bottom.
First of all I assumed there are n boxes and started counting from the bottom but with a difference, n would be the bottom most n-1 would be 2nd last and 1 would be the topmost
I can start counting from the top also, 1, 2, .... n
Now the question says 16th box from bottom (n-15 according to first method of counting) is exacly above 20 th from top (No 20 according to 2nd method of counting).
Since both the numbering are the same 20th box from top would have 20 in it either way you count it
ie
20 = (n-15+1)
=> n= 34
Always borrow money from a pessimist, he doesn't expect to be paid back.
