1. **Stating the problem:** We need to find the length of the side $CD$ of the quadrilateral $ABCD$ given the coordinates of points $C$ and $D$. 2. **Formula used:** The distance between two points $C(x_1, y_1)$ and $D(x_2, y_2)$ in the coordinate plane is given by the distance formula: $$ CD = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2} $$ 3. **Identify coordinates:** From the description, assume the coordinates of $C$ and $D$ are known or can be read from the graph. For example, if $C = (x_C, y_C)$ and $D = (x_D, y_D)$. 4. **Calculate the differences:** Calculate $\Delta x = x_D - x_C$ and $\Delta y = y_D - y_C$. 5. **Calculate the length:** Substitute into the formula: $$ CD = \sqrt{(\Delta x)^2 + (\Delta y)^2} $$ 6. **Simplify the square root:** Extract the largest perfect square factor from under the root if possible. 7. **Final answer:** The length $CD$ is the simplified value obtained. Since the exact coordinates are not provided in the message, please provide the coordinates of points $C$ and $D$ or confirm them from the graph to calculate the exact length.