1. **State the problem:** Solve the system of equations given by: $$x = y$$ $$4x + 9y = -39$$ 2. **Use substitution:** Since $x = y$, substitute $y$ with $x$ in the second equation: $$4x + 9x = -39$$ 3. **Combine like terms:** $$13x = -39$$ 4. **Solve for $x$:** $$x = \frac{-39}{13}$$ Show cancellation: $$x = \frac{\cancel{-39}}{\cancel{13}} = -3$$ 5. **Find $y$:** Since $x = y$, then: $$y = -3$$ **Final answer:** $$x = -3, \quad y = -3$$