I'm using just over four gallons per acre with mostly corn on corn.  That gets the corn grown and put into the bin.  Yes, I would have known about what it took at 20 as well.  Numbers like that got several test runs in term projects for several different classes.  I might not have had a quick number off the top of my head at the time because I would have been too caught up in trying to decide if it was something like 4.07 gallons or 4.08 gallons.  Later I learned the rest of the world would pass me by if I was to keep spending so much time splitting hairs.

I wanted to farm for a living.  Most people were not very optomistic about farming at the time.  What things were going to cost and the variability of outcomes was very much on my mind at age 20.  I think several of my peers were the same in those regards.