It mean that you can look in the past (hindsight) and see what you did wrong. Perfect vision is 20/20. So as you look back, you're able to see "perfectly" what you should have done. "Hindsight is...
20/20 vision is when you can see things without difficulty from 20 feet away. It's average vision.
It refers to the 2nd version/generation of the internet.
It means less then 21 yet more than 19.20 refers to the power of the tractor not the age
Add up all the numbers together and then divide by 12 to find the average mean:-68/12 = 17/3 or as 5 and 2/3