Answer
Find out the how many traffic lights are there on elm street .
To prove
As given
Elm street is 3.6 kilometers Long .
There are sets of 4 traffic lights every 0.6 kilómeter.
i.e

Now
Traffic light in 3.6 kilometers = Traffic light in one kilometer × 3.6

Traffic light in 3.6 kilometers = 24
Therefore Traffic light in 3.6 kilometers are 24 .