9-5

$${x_\text{mk}=\frac{1}{M} \sum_{i=1}^n m_i x_i, \quad y_\text{mk}=\frac{1}{M} \sum_{i=1}^n m_i y_i,\quad z_\text{mk}=\frac{1}{M} \sum_{i=1}^n m_i z_i}$$