Let N,O be functions such that N(x) = 2/sqrt(x), and O(x) = x^2. What is N(O(N(O(N(O(3))))))?
Start by evaluating O(3) in the middle and working outwards. It's a tedious problem, but straightforward.
O(3) = 3^2 = 9
N(9) = 2/sqrt(9) = 2/3
O(2/3) = 4/9
and so on.