The correct option is A 150 J
Mass of barbell, m = 5 kg
Height of lift, h = 3 m
Force require to lift the barbell = Weight of the barbell
Weight of the barbell =m×g
Work done by boy, W=Force×Displacement
=50×3=150 Nm or J
Work done is positive as both force and displacemnet are in the same direction.