A circular hole of $25 \: mm$ diameter and depth of $20 \: mm$ is machined by EDM process. The material removal rate (in $mm^3/min$) is expressed as $$4 \times 10^4 \: IT^{-1.23}$$ where $I=300 \: A$ and the melting point of the material, $T=1600^{\circ}C$. The time ( in minutes) for machining this hole is _________ (correct to two decimal places)