1. The problem asks about the slope of vertical and horizontal lines. 2. The slope of a line is defined as the change in $y$ divided by the change in $x$, or $$m=\frac{\Delta y}{\Delta x}$$. 3. For a vertical line, the $x$-coordinate is constant, so $$\Delta x=0$$. 4. Substituting into the slope formula, we get $$m=\frac{\Delta y}{0}$$ which is division by zero and undefined. 5. For a horizontal line, the $y$-coordinate is constant, so $$\Delta y=0$$. 6. Substituting into the slope formula, we get $$m=\frac{0}{\Delta x}=0$$. 7. Therefore, the slope of a vertical line is undefined, and the slope of a horizontal line is 0. Final answer: The slope of a vertical line is undefined, and the slope of a horizontal line is 0.