Answer:
The mass of the piece of Mg ribbon is 0.056g.
Step-by-step explanation:
1st) It is necessary to calculate the volume of the Mg ribbon:

The volume is 32mm^.
2nd) With the volume and the density, we can calculate the mass of the Mg ribbon. It is important to convert first the mm^ to cm^: ()32mm^3=0.032cm^3

So, the mass of the piece of Mg ribbon is 0.056g.