Step 1:

Combinations of $\"\"$ objects 1, 2, 3 and 4 taken 3 at a time are,

$\"\"$ .

The combination is $\"\"$ .

Formula for number of combinations of $\"\"$ , taken $\"\"$ at a time is given by,

$\"\"$ .

Where $\"\"$ , $\"\"$ .and

$\"\"$ .

Substitute $\"\"$ and $\"\"$ in the combination formula.

$\"\"$

Solution:

$\"\"$