Step-by-step explanation:
It is given that,
Speed of sound, v = 750 miles per hour
Since, 1 miles/hour = 1.46 foot/second
So, the speed of sound, v = 1100 feet/second
It takes about 3 seconds to hear the echo, t = 3 seconds. Let the canyon wall is d feet away. It can be calculated as :


d = 3300 feet
Echo is the repetition of sound. So, the canyon wall is 3300/2 = 1650 feet away. Hence, this is the required solution.