Find a vector parametric equation r(t) for the line through the points P = (-5,1,5) and Q = (-5,5,4) for each of the given conditions on the parameter t.
(a) If r(0) = (-5,1,5) and r(2) = (-5,5,4), then r(t)
(b) If r(3) = P and r(6) = Q, then r(t)
(c) If the points P and Q correspond to the parameter values t = 0 and t = -4, respectively, then r(t)