I don’t know why they died, they just died.
After the students plant orange trees as a class project, the trees die. Edgar cannot give a reason for why they die. He mentions the possibility of poor soil or low-quality trees, but these are just guesses. All he knows with any certainty is that the trees died. The author uses just as an adverb meaning “simply” or “absolutely” to emphasize the verb died. As an adjective, though, just can mean “fair” or “impartial.” Since death is inescapable, the tree’s death can be seen as fair or impartial. It is not right or wrong that the trees die. It just is.
As soon as I saw the puppy I thought, Oh Christ, I bet it will live for about two weeks and then . . . And that’s what it did.
The Murdoch girl brings the puppy to school. She found it underneath a delivery truck and was afraid that the truck would run it over. Based on prior experience with animals in the classroom, Edgar imagines that the puppy will die soon. Despite the Murdoch girl’s effort, she is unable to save the puppy from death. She only manages to defer the puppy’s death, which the narrator recognizes as inevitable.