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