An iron casting weighs 27kg in air 18kg in water. What is the volume of the covities in the casting ? (Density of iron `=7800kgm^(-3)`)
A. outer volume of casting is `6000 cm^(3)`
B. outer volume of casting is `9000 cm^(3)`
C. volume of cavity inside the casting is `780 cm^(3)`
D. volume of cavity inside the casting is `5538 cm^(3)`
