11. Hikers at the bottom of a canyon are facing towards the canyon wall 280.5 meters away. Given that the speed of sound in air is 340 m/s, how long after they should will they hear their echo? 12. A child on a toboggan slides down a snowy hill, accelerating uniformly at 2.8 m/'s2. When the toboggan passes the first observer, it is travelling with a speed of 1.4 m/s. How fast will it be moving when it passes a second observer, who is 2.5 m downhill from the first observer? Show all work as demonstrated in the lessons