First find the mass.
Since weight force is 48N, and acceleration due to gravity is 9.8 m/s^2,
weight force = mass*acceleration due to gravity,
mass = weight/acceleration
mass = 48N / 9.8 m/s^2
mass = 4.9 kg
Now you find the force needed to accelerate to 3.0 m/s^2.
Force = mass*acceleration
Force = 4.9kg * 3.0 m/s^2
Force = 14.7 N