Two children setup a "telephone" by placing a long, slender aluminum (Y = 6.9 1010 N/m2) bar that has a length of 6.1-m between their two houses.

Two children setup a "telephone" by placing a long, slender aluminum (Y = 6.9 × 1010 N/m2) bar that has a length of 6.1-m between their two houses. To communicate, a child taps a coded message on one end. How long do the sound waves take to reach the other end? Note: the density of aluminum is 2700 kg/m3.