Calculate the void volume in an $fcc$ unit cell if the total volume of the unit cell is $6.4 \times 10^{-23} \text{ cm}^3$.

• A
  $3.172 \times 10^{-23} \text{ cm}^3$
• B
  $3.911 \times 10^{-23} \text{ cm}^3$
• C
  $1.664 \times 10^{-23} \text{ cm}^3$
• D
  $2.051 \times 10^{-23} \text{ cm}^3$