\[{\overline{C}\ }_{4}^{3} = \frac{(3 + 4 - 1)!}{3!(4 - 1)!} = \frac{6!}{3! \bullet 3!} =\]
\[= \frac{6 \bullet 5 \bullet 4 \bullet 3!}{3 \bullet 2 \bullet 3!} = 5 \bullet 4 =\]
\[= 20\ способов.\]
\[Ответ:\ \ 20.\]