We have 12 km / 3 km = <<12/3=4>>4. So, the distance covered in 12 km is 4 times greater than 3 km. The time taken will also be 4 times greater.
So, 2 hours x 4 = <<2*4=8>>8 hours.
We convert the time to minutes: 8 hours * 60 minutes/hour = <<8*60=480>>480 minutes.
#### 480