20. If $x_q = \alpha_q i + \beta_q j + \gamma_q k \in \mathbb{R}^3$, $q = 1, 2, ..., n$, are any $n$ vectors, show that
$\sum_{q=1}^{n} x_q = \left(\sum_{q=1}^{n} \alpha_q \right) i + \left(\sum_{q=1}^{n} \beta_q \right) j + \left(\sum_{q=1}^{n} \gamma_q \right) k$
$= \left(\sum_{q=1}^{n} \alpha_q, \sum_{q=1}^{n} \beta_q, \sum_{q=1}^{n} \gamma_q \right)$.