given , 
Mass of sample of cobalt = 27 g
density of sample of cobalt = 9g/cm^3
We know that , 
Density = mass of sample/volume of sample 
From that relation , 
We can deduce the following as 
Volume = mass of sample/density of sample 
Hence , required volume of sample of cobalt = 27 g /9 g/cm^3 = 3 cm^3
The volume is [tex]\fbox{3cm cube}[/tex]