Which system of equations has only one solution?
4 x + 2 y = 8. Negative 4 x minus 2 y = 3.
Negative 5 x + y = 6. 5 x minus y = negative 6.
Negative 3 x + 4 y = 2. 3 x minus 4 y = 0.
2 x + 4 y = 6. 3 x minus 4 y = 9.

Sound travels about 750 miles per hour. a) suppose it takes about 1.5 seconds to hear the echo. how far away is the canyon wall, in feet? for this i got 825 ft b) suppose you stand 1,925 feet from the canyon wall and sound the horn. how long will it take to hear the echo? (i'm stuck on this)