Answer:
The person responsible for purchasing Alaska was William Seward.
Explanation: He bought it from Alaska and many people thought it was a mistake so they called it '' Seward's Folly.''
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,
$\frac32=\frac{220}{8\times3\times d}$
$\implies d=\frac{55}9=6.12$
I would say the answer is a