Acar is traveling at a constant speed of 12m/s , when the driver accelerates the car reaches a speed of 26 m/s in 6s what is the acceleration of the car

The stopwatch used by a student to measure velocity of a pulse in a slinky was of least count 0.1 second. he stops the stopwatch when a pulse has made 3 journeys from one end to the other of the slinky. he finds the seconds hand to be at 52nd division. calculate the correct time noted by him.