A speedboat starts from rest and accelerates at +1.94 m/s2 for 7.00 s. At the end of this time, the boat continues for an additional 6.00 s with an acceleration of +0.515 m/s2. Following this, the boat accelerates at -1.58 m/s2 for 8.00 s. What is the velocity of the boat at t = 21.0 s?