A train approaches a small town with a constant velocity of
+28.6 m/s. The operator applies the brake, reducing the train’s
Velocity to +11.4 m/s. If the average acceleration of the train during
Braking is –1.35 m/s2, for what elapsed time does the operator apply
The brake?

you need to solve 28.6 - 1.35t = 11.4 for t