Find the optimal working width for a row$-$planting machine that is intended to be used for cultivating an area of $150$ hectares, operating at a speed of $6\mathrm{.}5$ km$/$h$,$ and with a field efficiency $($Ef$)$ of $75\%.$ The price of this machine is $6000$ SAR, and the tractors operating cost $($T$)$ is $10$ SAR$/$hour$.$ The labor wages are $12$ SAR$/$hour$,$ and the fixed annual costs are $6\%$ of the machines purchase price.$W=\sqrt[\phantom{2}]{\frac{100**10**A}{(FC\%)**P**S**E_f}(L+T)}$