Step-by-step explanation:
[tex]area = \frac{1}{2} a.b \sin(C) \\ from \:cosine \: rule \\ {c}^{2} = {a}^{2} + {b}^{2} - 2a.b \cos(C) \\ 36 = 144 + 81 - (2 \times 12 \times 9) \cos(C) \\ 189 = 216 \cos(C) \\ \cos(C) = 0.875 \\ C = \cos {}^{ - 1} (0.875) \\ C = 28.96 \degree \\ area = \frac{1}{2} \times 144 \times 9 \times \sin(28.96 \degree) \\ area = 313.8 \: sq \: units[/tex]
