A jet plane is cruising at 300 m/s when suddenly the pilot turns the engines up to full throttle. After traveling 4.0 km, the jet is moving with a speed of 400 m/s.What is the jet's acceleration, assuming it to be a constant acceleration? first i converted 4km to m. then i said that since at first he was traveling 300m/s, it must of taken him about 13.33 seconds to reach 400m/s. then i followed the formula for average acceleration, which is vf-vi/tf-ti, and i get a wrong answer. what am i doing wrong?