An echo in Cowboys Stadium is heard after 2 seconds. How far is the person standing from the wall if the speed of sound is 340 m/sec?

d=velocity (velocity divided by time)

Time

So, what you're trying find is distance.
Now, just fill in the equation with your data
d?=340m/s
2seconds
D= 170m
Remember that because you have seconds on both sides of the line ( division) they cancel out each other and you're left with meters. I just did something similar to this in physics class not too long ago. Hope this helps