A particle starts at the point $P=(-4,1,-5)$ and moves along a straight line toward $Q=(-2,4,-7)$ at a speed of 6 cm/sec. Let $x$, $y$, $z$ be measured in centimeters and $t$ be measured in seconds.

(a) Find the particle's velocity vector.
$\vec v(t) =$

(b) Find parametric equations for the particle's motion.
$x(t) =$ ,
$y(t) =$ ,
$z(t) =$