$(4\mathrm{.}1)$ A thin layer of radioactive $^110$ Ag is deposited at the end of a silver bar, which was held at $800^$ C for $48$ hours. The bar is then mechanically sectioned$,$ and the radioactivity of each section is measured. The measured data for count rate, in counts per minute $($cpm$),$ versus distance from the end of the bar, x$,$ are as follows:

x$(\backslash$mu m$)$ Count Rate $($cpm$)$

$24000$

$43900$

$63550$

$83230$

$102870$

$122460$

Plot the data and determine the self$-$diffusion coefficient of silver, D$\_$Ag$,$ at $800^$ C$.$ Report the diffusion coefficient in units of cm$^2/$s$.$