9.1.20 Double integrals

Problem: Find the double integral over the given area \( D \) : \[ \iint_{(D)}(12-2 x-3 y) d x d y, \quad D:\left\{\begin{array}{l} 12-2 x-3 y=0 \\ x=0, \quad y=0 \end{array}\right. \]