Math Word Problem

(For those who can't read what is on the picture)
A train 1000 meters long travels through a tunnel 3000 meters long. 30 seconds pass from the time that the last car just completely entered the tunnel until the time when the front of the engine emerges from the other end.

Determine the speed of the train when it travels in kilometers per hour.

Step 1: What is important from the question?

What I know
-The train is 1000 meters long
-The train went through a 3000 meter tunnel in 30 seconds

What I want to know
-What is the speed of the train when it travels in kilometers per hour?

Step 2: Let's make a plan!

Okay, the question is asking me to find out how much time it will take for the train to travel a kilometer. So what I need to do first, is that find out how much distance is covered in a second. In order to do that I can do the equation: 3000 meters/30 seconds. The reason why i would need to do that is that, once I found out how much distance is traveled in a second I will multipluy that by 60 since there are 60 seconds in 1 minute. Whatever I multiply to the top of the fraction, I have to multiply the bottom too, so I'll multiply both the meters and the seconds by 60. After that, since I have it for per minute, I need to turn it into meters/kilometers per hour. So I will multiply by 60 to the numerator and the denomanator so that the fraction can still reduce to the seconds and for us to find out how many kilometers is traveled in 1 hour.

Step 3: Now that we have a plan, let's see if it works!

3000 meters  =  100 meters
30 seconds    =  1 second

Now to find it per minute...

100 meters ×60 = 6000 meters                
1 second     ×60 = 60 seconds/1 minute

Now to find it per hour

6000 meters ×60 =  120000 meters       
1 minute        ×60 =  60 minutes/1 hour

Step 4: Let's check to see if I'm right...(I hope I am)

120000 meters ÷60 = 6000meters
1 hour                 ÷60 = 1 minute

6000 meters ×60 = 100 meters
1 minute        ×60 = 1 seconds

This proves that the train will travel 120,000 meters/120 kilometers per hour.

Step 5: Conclusion, our final statement

In conclusion, the train will travel 120km per hour.