#### Answer

$2$; $8$

#### Work Step by Step

Note that $16=2^4$.
RECALL:
$a^{\frac{m}{n}}=(\sqrt[n]{a})^m$.
Use the rule above:
$16^{\frac{3}{4}}
\\=(\sqrt[4]{16})^3
\\=(\sqrt[4]{2^4})^3
\\=(2)^3
\\=8.$
Thus, the missing expressions are $2$ and $8$.