It is given that Mr Martin takes 12 minutes to drive his bus route without stopping on any of the stops.
On Tuesday, it took him 14 minutes when he stooped to take the passengers. He estimated that it takes 30 sec for each stop.
60 second = 1 minute.
30 second = 0.5 minutes.
Let us assume, there were x stops.
Since it takes him 12 minutes without stopping, 12 minutes here acts as a fixed time.
Total time is given by the equation
.... (1)
where t is the total time and x is the number of passengers.
To find the number of passengers, solve equation (1) for x ,
.... (2)
Plug y= 14 into equation number (2) gives 4 stops.