The density of any object can be derived by dividing its mass by its volume. Density is expressed in units like kg/m^3, g/cm^3, etc.
Here the mass of the brick of salt is 321 g.
The dimensions of the brick are 5 cm x 5 cm x 2.5 cm. This gives the volume of the brick of salt as 5*5*2.5 = 25*2.5 = 62.5 cm^3
The density is 321/62.5 = 5.136 g/cm^3
The density of the brick of salt is 5.136 g/cm^3
We'll recall the formula that gives the density of a substance:
Density = mass/Volume
Since the mass is given, we'll have to calculate the volume of the brick of salt:
V = length*width*height
V = 5*5*2.5
V = 62.5 cm^3
Now, we'll determine the density:
Density = 321/62.5
Density = 5.136 g/cm^3
The requested density of the brick of salt is Density = 5.136 g/cm^3.