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