$\"\"$

\

The combination is $\"\"$ .

\

The combinations formula is $\"\"$ .

\

$\"\"$ (Apply combinations formula)

\

$\"\"$ ( $\"\"$ ) $\"\"$

\

$\"\"$ (Expand $\"\"$ )

\

$\"\"$ (Cancel common terms) \ \

\

$\"\"$ . (Multiply: $\"\"$ ) $\"\"$

\

The total number of combinations are 210.