Two rods A and B of lengths 100 m each are joined end to end. Velocity of sound in A is $$800\text{ m/s}$$. Young's modulus ($$Y$$) and density ($$d$$) of B are two and eight times of their respective values of A. Find the time taken (in s) by sound to travel between the free ends of the rods. (Velocity of sound in the rod is $$v = \sqrt{\frac{Y}{d}}$$)