Answer :
The time it takes to hear an echo can be gotten from the equation;
[tex]t=\frac{2D}{v}[/tex]Where D is the distance to the wall, v is the speed of sound which is 750 miles per hour.
If it takes 3 seconds to hear an echo, the distance can be gotten by rewriting the equation as;
[tex]D=\frac{vt}{2}[/tex]Therefore, we find out that;
[tex]D=\frac{750\times3}{2}=1125\text{miles.}[/tex]Therefore, the wall is 1125 miles away.
b. To generalize the result;
If it takes n seconds to hear an echo, the distance to the canyon wall is;
[tex]D=\frac{750n}{2}=375n[/tex]Therefore, D = 375n