Abox of mass 3.0 kg is accelerated from rest across a floor at a rate of 3.0 m/s2 for 4.0 s . what is the net work

Work done is given by multiplying force and distance.
Therefore; W = Force × distance
  but from the second newton's law of motion F=ma
Therefore; W = (ma) × d
Using; V= U + at
 V = 0 + (3×4)
 V = 12 m/s
 But d = (V+U)/2 (t)
        d = 12/2 (4)
           = 24 M
Hence;  W = ( 3 ×3 )× 24
                  = 216 J

You get 6 for mechanical

The low lands i believe