Since the acceleration is constant we know that it is given by:
![a=(v_f-v_0)/(t)](https://img.qammunity.org/2023/formulas/physics/college/sya85zlwdlif7vi37exkjvpvdur62il7ec.png)
from where we have that:
![t=(v_f-v_0)/(a)](https://img.qammunity.org/2023/formulas/physics/college/kqv3bmokcjrccxpzera9a915mi1zzhpk6c.png)
once we have this equation we can determine the time by plugging the values of the acceleration and velocities.
a)
In this case we have that:
![t=(31.5-21.5)/(3.74)=2.67](https://img.qammunity.org/2023/formulas/physics/college/ex88vj8kdpclt000skin6ikjriyev7zolq.png)
Therefore it takes 2.67 s.
b)
In this case we have that:
![t=(61.5-51.5)/(3.74)=2.67](https://img.qammunity.org/2023/formulas/physics/college/qdutzqtxvngi8jrvej3c4j4wcxxi1y7ffw.png)
Therefore it takes 2.67 s.