Let \( P \) be the set of seven digit numbers with sum of their digit equal to \( 11 \). If the numbers in \( P \) are formed by using the digits \( 1 \), \( 2 \) and \( 3 \) only, then the number of elements in the set \( P \) is:
\( 173 \)
\( 158 \)
\( 164 \)
\( 161 \)