Over a time interval of 2.04 years, the velocity of a planet orbiting a distant star reverses direction, changing from +18.2 km/s to -22.9 km/s. find (a) the total change in the planet's velocity (in m/s) and (b) its average acceleration (in m/s2) during this interval. include the correct algebraic sign with your answers to convey the directions of the velocity and the acceleration.