Chapter 12 - Parametric Equations, Polar Coordinates, and Conic Sections - 12.2 Arc Length and Speed - Exercises - Page 611: 17

$$\sqrt{41 } $$

Since speed given by \begin{align*} \frac{d s}{d t}&=\sqrt{x^{\prime}(t)^{2}+y^{\prime}(t)^{2}}\\ &=\sqrt{25+16 } \end{align*} Then \begin{align*} \frac{d s}{d t}\bigg|_{t= 9} &=\sqrt{25+16 } \\ &=\sqrt{41 } \end{align*}