A4 Curves: Problem 6 Previous Problem Problem List Next Problem (1 point) Let r(t) = (t2, 1 - t, 4t). Calculate the derivative of r (t) . a(t) att = 4, assuming that a(4) = (2, -9, 3) and a' (4) = (-9, 6, -5) d dt r(t) . a(t) |t-4 =