For this case we must find an expression equivalent to:
[tex]16 ^ {\frac {3x} {4}}[/tex]
By definition of properties of powers and roots we have:
[tex]a ^ {\frac {m} {n}} = \sqrt [n] {a ^ m}[/tex]
Then, we can rewrite the expression as:
[tex]\sqrt [4] {16 ^ {3x}}[/tex]
Answer:
[tex]\sqrt [4] {16 ^ {3x}}[/tex]