How many unit cells are present in 39g of potassium that crystallizes in a BCC structure

I don't understand the method of solution???

Atomic mass of potassium is 39 g.

In a BCC unit cell, there are 8 atoms at the corner of a cube and 1 atom at the centre.

Number of atom per unit cell =

8 x 1/8 + 1 x 1 = 2

Number of atoms in 39 g of potassium = 39/39 x 6.02 x 10²³
[N is the Avogadro number = 6.02 x 10²³]
So, Number of unit cells in 39 g of potassium = 39/39 x 6.02 x 10²³/2 = N/2 unit cells