In order to covert a unit, you must know certain number of conversions. In here, the conversion is in unit of length. One meter is equal to 1000 meter. So if it is in cubic form, then the answer of one meter cube is also equal to 1000 cube. Then,
32 m³ (1000 mm/1m)³
or
32 m³ (1000³ mm³/1 m³)
= 3.2 x 10¹⁰ mm³