The equation of the parabola is given in general form. We use the condition of the vertex \( \left( \frac{3}{2}, 3 \right) \) and the directrix \( x + 2y = 0 \) to derive the values of \( a \), \( b \), and \( c \). Then, we calculate \( \alpha + \beta + \gamma \).
Final Answer: \( \alpha + \beta + \gamma = 6 \).