Answer: 70 minutes
Step-by-step explanation: simply do 420/6 to find out the number of minutes it will take.
You could also do this as a ratio of minutes to cartons 1:6 and find out how many times you must multiply 6 cartons to get to 420 cartons. That number is 70 so just multiply the 1 for the number of minutes because in ratios you must multiply by the same value for each number in the ratio.