Kinematic problem~~~

A car is traveling along a straight road at a velocity of +31.0 m/s when its engine cuts out. For the next ten seconds, the car slow down, and its average acceleration is ā1. For the next five second, the car slow down further, and its average acceleration is ā2. The velocity of the car at the end of the fifteen-second period is +24.5 m/s. The ratio of the average acceleration values is ā1/ā2=1.67. Find the velocity of the car at the end of the initial ten-second interval.