Answer
a. $(5,1500)$ and $(12.2,1500)$.
b. $(0,15)$
Work Step by Step
a. The solutions are the intersections of $y=1500$ with the curve at $x=5\ in$ and $x=12.2\ in$, as indicated in the figure with points $(5,1500)$ and $(12.2,1500)$.
b. As volume needs to be positive, based on the graph, a realistic domain would be $0\lt x\lt 15\ in$ or $(0,15)$
