This is the 304th most frequent Dutch word.
viel
"Viel" is the past tense of "vallen," meaning "fell."
In this sentence, 'viel' is the past tense of the verb 'vallen', meaning 'to fall'.
Hij viel van de trap.
He fell down the stairs.
Here, 'viel' is used in a figurative sense to indicate that the assignment 'was' easy to grasp—the verb 'vallen' in Dutch sometimes conveys subjective ease or difficulty.
De opdracht viel makkelijk te begrijpen.
The assignment was easy to understand.
'Viel' in this instance is part of the phrase 'opvallen', meaning 'to notice' or 'to stand out', indicating a form of realization.