A ball rolls off the top of a stairway with a velocity u. If the height of each step is h, the breadth is b and the ball hits the edge of nth steps, the find the value of n.

Question

$\begin{array}{1 1}(A)\;2hu \\(B)\;\frac{2hu^2}{gb^2} \\(C)\;\frac{1}{2}hu\\(D)\;0 \end{array}$