$1\mathrm{.}9$ Consider the air over acity to be a box $100$ km on aside that reaches up to an altitude of $1\mathrm{.}0$ km $.$ Clean air is blowing into the, box along one side of its sides arith a speed of $4\frac{m}{s},($Fig $3).$ Suppase an air pollutant with reaction rate $K=0\mathrm{.}2dhr$ is emitted into the box at at total rate of $10k\frac{g}{s}.$ Find the steadystale conen' $f$ the air is assumed to be completelymixed

Fig$3$