To solve this problem, we can calculate for the milligrams of remaining acetaminophen by multiplying the volume with the concentration.
Remaining acetaminophen after 2 hours = Concentration after 2 hours * Volume
Where, concentration = 8 mcg / mL = 8 cg / L
volume = 51 L
Remaining acetaminophen after 2 hours = (8 cg / L) * (51 L) = 408 cg
ANSWER: 408