Answer:
Average speed(S) is given by:
....[1]
where,
D is the total distance and t is the time.
As per the statement:
A gazelle that runs 140 meters in 5.0 seconds.
⇒D = 140 meters and t = 5 seconds
Substitute in [1] we have;

Simplify:
⇒S = 28 m/sec
Therefore, average speed of a gazelle is, 28 m/sec