Answer:
1) 1.5 m/s^2
2) 4.5 N
Step-by-step explanation:
From Newton's Second Law of motion, we know

Which states that to calculate the force acting on an object, you multiply its mass and acceleration.
So, we know an object of mass 1.5 kg has an acceleration of 3 m/s^2, then

A force of 4.5 N is acting on the object.
If a force of 4.5 N acts on a mass of 3kg we have

So, it would give it an acceleration of 1.5 m/s^2.