In an aeration system where the total head is assumed to be $1\mathrm{.}0$ meters, $1\mathrm{.}11m\frac{g}{L}{O}_2$ is

consumed to oxidize organic materials. Since the net oxygen level at the end of the

second step in the cascade aerator designed as a two$-$stage is found to be $7\mathrm{.}5m\frac{g}{L},$

calculate the initial dissolved oxygen concentration of the water $(T=10C).$