Answer:
40 seconds
Step-by-step explanation:
A unicorn is running at rate of 3 meters/second. To find how long it'll take to get at the end of a 120 meter rainbow, we'll have to find the "time".
The distance is given to be 120 meters and speed is given as 3 meters/second.
Our formula for speed is:

where v is speed, s is distance and t is time:

Solve for t, multiply both sides by t:

Divide both sides by 3:

Therefore, it will take 40 seconds for a unicorn to reach at the end of rainbow.