\binom{5}{2} = \frac{5 \cdot 4}{2} = 10,\quad \binom{7}{2} = \frac{7 \cdot 6}{2} = 21,\quad \binom{12}{4} = \frac{12 \cdot 11 \cdot 10 \cdot 9}{4 \cdot 3 \cdot 2 \cdot 1} = 495