Answer:
We know that the mass of the box is m = 400g, then the weight of the box is equal to the gravitational acceleration times the mass, this is:
w = -9.8*0.4N = 3.92N downwards
Where i used 0.4kg instead of 400g, because the units are easily calculated in kg than in grams. This calculation is obtained by knowing that 1000g = 1kg, then 400g is equal to (400/1000)kg
Now, if you want to lift the box, you need to cancel this force, so you should use a force of at least 3.92N upwards.
And the work is defined as the movement done by a force, and can be calculated as:
W = F*d
in this case the minimal force is F = 3.92N, and the distance is d = 6.0m
And we have W = 3.92N*6.0m = 23.52 joules
