........was connected to the great lakes by the opening of the Erie Canal.
assuming efficiency of each man to dig trench, in one day, for one hour is constant,

so one man, working for one hour in one day can dig 1.5 m
so 8 men, working 3 hours a day and will take, say $d$ number of days and efficiency will be constant. so,
$\frac32=\frac{220}{8\times3\times d}$
$\implies d=\frac{55}9=6.12$
It was the battle of the bulge.
Men were chosen by the draft. You had to sign up and if your number was picked - you left for Vietnam
The only way to get out of the draft was to have a medical deferment, move to Canada or stay in college.
Donald trump had 5 medical deferments for bad feet
We should know about this because American Citizens need to know how we won the war.