$7\mathrm{.}4$ In Problem $7\mathrm{.}3$ above, consider the same smelter to be on level, open ground. The stack is $200$ m tall and the plume rise is $100$ m $.$ The wind is $4\frac{m}{s}$ and the stability class is C $.$ Estimate the ground$-$level $S{O}_2$ concentration $6,000m$ directly downwind. What is the concentration $300$ m off the centerline at this same $x$ value?

$7\mathrm{.}3$ Wind blows down a trapezoidal valley at $8\frac{m}{s}.$ The valley depth is $800$ m $,$ the floor width is $1,000m,$ and the width at the top is $2,000m.$ A smelter emits $S{O}_2$ at a steady rate of $10,000k\frac{g}{?}$ day. The valley is capped by an inversion. Calculate the steady$-$state concentration a long way downwind from the smelter, where the pollutant is uniformly spread across the width and height of the valley.

$7\mathrm{.}4$ In Problem $7\mathrm{.}3$ above, consider the same smelter to be on level, open ground. The stack is $200$ m tall and the plume rise is $100$ m $.$ The wind is $4\frac{m}{s}$ and the stability class is C $.$ Estimate the ground$-$level $S{O}_2$ concentration $6,000m$ directly downwind. What is the concentration $300$ m off the centerline at this same $x$ value?