b) 21 m³ (cm³)
13 m³ (mm³)
331 (cm³)
2 400 hl (m³)

b) 21 m³ (cm³) = 21000000 cubic centimeters

13 m³ (mm³) = 13,000,000,000 cubic millimeters

331 (cm³) = 0.331 cubic meters

2,400 hl (m³) = 240 cubic meters