A T- ask is seeded with $10^5$ anchorage-dependent cells. The available area of the T- ask is $25\: cm^2$ and the volume of the medium is $25\: ml$. Assume that the cells are rectangles of size $5\: \mu m \times 2\: \mu m$. If the cells grow to monolayer confluence after $50\: h$, the growth rate in number of $cells/(cm^2 .h)$ is _________$\times10^5$