1. **State the problem:** Convert the standard form equation $x + y - 3 = 0$ to slope-intercept form $y = mx + b$. 2. **Recall the formula:** The slope-intercept form is $y = mx + b$, where $m$ is the slope and $b$ is the y-intercept. 3. **Isolate $y$:** Starting with $x + y - 3 = 0$, add $-x + 3$ to both sides: $$y = -x + 3$$ 4. **Interpret the result:** The slope $m = -1$ and the y-intercept $b = 3$. 5. **Graph description:** The line crosses the y-axis at $(0,3)$ and has a slope of $-1$, so it goes down one unit for every one unit it moves right. **Final answer:** $$y = -x + 3$$