Answer:
Vo = 4.5 [m/s]
Step-by-step explanation:
In order to solve this problem, we must use the following equation of kinematics.

where:
Vf = final velocity = 12 [m/s]
Vo = initial velocity [m/s]
a = acceleration = 1.5 [m/s²]
t = time = 5 [s]
Now replacing:
![12=v_(o)+1.5*5\\v_(o)=12- (7.5)\\v_(o)= 4.5[m/s]](https://img.qammunity.org/2022/formulas/physics/college/wbc4evtrz3wgsgbtgimyj45wpuw2u2ineq.png)