Complete question is
It takes a truck 3.56 seconds to slow down from 112 km/h to 87.4 km/h. What is its average acceleration?
To convert km/h into m/s multiply by 5/18
Initial velocity =u=112 km/h=112*5/18 m/s = 31.1 m/s
Final velocity=v=87.4 km/h= 24.2 m/s
Time=3.56 secs
Average acceleration = change in velocity/time
=
=
=
=1.94 m/s²