The equivalent to 16^(3/4x) is ⁴ˣ√16³.
It reads, 4x root of 16 raised to the power of 3.
16^(3/4x) can be written like this: (16³)^1/4x
1/4x as an exponent means the 4x root of the base number.
3 as an exponent simply means that the base number is raised to the third power.