Hello, Alessandra,
The volume of the dilithium is calculated by dividing it's mass by it's density:
(867.5 grams)/(0.534 grams/ml) = 463 ml to 3 sig figs
Use the units to help guide the calculation required. The grams cancel and units moves to the top. Density could be in ml, cm3, or other unit - the volume will simply be that unit.
Bob