1. **State the problem:** Find the equation of the line given the x-intercept $a = -1$ and y-intercept $b = -3$. 2. **Formula:** The intercept form of the line equation is $$\frac{x}{a} + \frac{y}{b} = 1$$ where $a$ is the x-intercept and $b$ is the y-intercept. 3. **Substitute the values:** $$\frac{x}{-1} + \frac{y}{-3} = 1$$ 4. **Simplify the fractions:** $$-x - \frac{y}{3} = 1$$ Multiply both sides by 3 to clear the denominator: $$3 \times \left(-x - \frac{y}{3}\right) = 3 \times 1$$ $$-3x - y = 3$$ 5. **Rewrite the equation:** $$-3x - y = 3$$ Multiply both sides by $-1$ to make the coefficients positive: $$\cancel{-1} \times (-3x - y) = \cancel{-1} \times 3$$ $$3x + y = -3$$ 6. **Final answer:** The equation of the line is $$3x + y = -3$$