Answer
The error is in the first step, turning $\frac{\sqrt[4] 16}{\sqrt 4}$ into $\sqrt[4] \frac{16}{4}$.
Work Step by Step
Because the we are taking the square root of 4 in the denominator of the first fraction and the fourth root of the 16 in the numerator, the numerator and denominator cannot be combined under a single radical.
