\({18 \choose 9}\text{.}\)
\(\binom{12}{7}\binom{6}{2} \text{.}\)
\(\displaystyle {18 \choose 9} - {3 \choose 1}{14 \choose 8}\)
\(\displaystyle {3\choose 1}{15 \choose 8} + {12 \choose 7}{6 \choose 2} - {3\choose 1}{9 \choose 6}{6 \choose 2}\)