First you find how many miles the car travels per hour, to do so you can divide 420 miles by 8 hours:
420 miles/8 hours = 52.5 miles/hr
Now that you know the car travels 52.5 miles per hour, you can multiply it by 12 to find out how many miles the car travels in 12 hours.
52.5 · 12 = 630
The car travels 630 miles in 12 hours
12 hours is 4 hours more than 8 hours.
4 hours is half of 8 hours.
If it traveled 420 miles in 8 hours, it will travel half of that in 4 hours, or 210 miles.
In 12 hours it travels 8 hours plus 4 hours, so it travels 420 miles plus 210 miles which is 630 miles.
Answer: 630 miles
