Concept: Graphing a linear inequality.

Explanation of the Correct Answer: The correct answer is C. Rewrite: $5y < -4x + 9$ → $y < -\dfrac{4}{5}x + \dfrac{9}{5}$. The slope is $-4/5$ (negative, line goes down). The $y$-intercept is $9/5$. Dashed line (strict $<$), shaded below the line.

Vietnamese Version: Khái niệm: Vẽ đồ thị bất đẳng thức tuyến tính. Giải thích đáp án đúng: Đáp án C. $y < -\dfrac{4}{5}x + \dfrac{9}{5}$. Đường nghiêng xuống, nét đứt, tô phía dưới.

Key Formula: $y < mx + b$ → dashed line, shade below.