A man moves along x axis such that velocity $v=\large\frac{1}{x}$. If he is initially at $x=2 m$ find the time when he reaches $x=4m$

Question

\[(a)\;6 sec\quad (b)\;4 sec \quad (c)\;3 sec \quad (d)\;he\;can't\;reach\; x=4m\]