\(\vec V = \frac{{{m_1}{{\vec u}_1} + {m_2}{{\vec u}_2}}}{{{m_1} + {m_2}}}\) \( = \frac{{1(3i - 2\hat j) + 2(4j - 6\hat k)}}{{{m_1} + {m_2}}}\)
\( = \frac{{3i + 6j - 12\hat k}}{{(1 + 2)}}\)\( = \hat i + 2\hat j - 4\hat k\)
\(|\vec V| = \sqrt {{{(1)}^2} + {{(2)}^2} + {{( - 4)}^2}} = \sqrt {1 + 4 + 16} = 4.6m{s^{ - 1}}\).