jmc

Let the radius be $r$ and the height be $h$. Since the lateral surface area is 3.5 square inches, we have $2\pi rh=3.5$. Since the volume is 3.5 cubic inches, we have $\pi r^{2}h=3.5$. Dividing the latter equation by the former, we find that $r=\boxed{2}$ inches.