Answer:
Aluminum
Explanation:
The density of Aluminum is 2.7 g/cm3 
We know the volume and mass of the unknown metal, as density is mass/volume:  81g/30cm3 = 2.7 g/cm3 which is the density of Aluminum :)
 
        
                    
             
        
        
        
Answer:
Recycle parts of old computers for their various metals.
Repurpose old computers for other needs.