\begin{aligned}
\text{rate} & = \frac{\text{length}}{\text{time}} \\
\\
&=\frac{90.4\  \text{cm}}{1 \ \text{day}}\\
\\
&=\frac{90.4\ \bcancel{\text{cm}}}{\bcancel{\text{day}}} \times\frac{10,000\ \mu m}{1\ \bcancel{\text{cm}}}\times \frac{1\ \bcancel{\text{day}}}{86400\ s}\\
\\
& = 10.5\ \mu m/s
\end{aligned}