An object moves such that its x-coordinate is given by x(t) = 6.0 m - (1.5 m/s2) t3 and its y-coordinate is given by y(t) = (8.0 m/s) t - (1.0 m/s2) t2. What is the acceleration of the object at t = 3.5 seconds? Express your answers in unit vector notation.