A set of four observations has mean \( 1 \) and variance \( 13 \). Another set of six observations has mean \( 2 \) and variance \( 1 \). Then, the variance of all these \( 10 \) observations is equal to:
\( 5.96 \)
\( 6.14 \)
\( 6.04 \)
\( 6.24 \)