For an electrochemical machining process
\[
\frac{dy}{dt}=\frac{\lambda}{y}-f ,
\]
where $y$ is the inter-electrode gap in mm at time $t$ (in minute), and $f$ is the feed of the tool in mm/minute. The value of $\lambda$ is $6\times10^{-3}$ cm$^{2}$/minute. For maintaining a constant inter-electrode gap of 0.1 mm, the feed (in mm/minute) should be \(\underline{\hspace{2cm}}\). [round off to one decimal place]