Welcome to the site, DeBee!!
Both recipes probably call for the use on one sack of flour (most likely 25 or 32 pound sacks). Most recipes start off with the flour being the main ingredient, then the rest of the ingredients are expressed as a percentage of the flour (called "Bakers Percentages").
Since a 25 (or 32) pound bag of flour is the norm, then that's my guess on the "100%" part of the equation. So, the "three tubs" of flour is most likely one sack of flour. But, I could be wrong.