For the first twenty years since yesterday
I scarce believed thou couldst be gone away;
For forty more I fed on favors past,
And forty on hopes that thou wouldst they might last.
Tears drowned one hundred, and sighs blew out two,
How is it possible that a person can go through twenty years in a day? 
 Keep in mind that this poem describes the progression of 24 hours using hyperbole, as every 100 years represents an hour of real time. Therefore, the first twenty years represents the first 12 minutes. Seeing as how the poem is titled “The Computation,” the passage of time within the poem involves the addition of increments as if time were an equation. 
 
 00:00 – 00:12 
 He introduces his conflict of dealing with the loss of a loved one, the first 12 minutes without them being spent in grief. The loss happened very suddenly and unpredictably, which explains why the speaker is still attempting the comprehend the situation.
The Computation