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M and L are total length and mass of the chain.
M = 4 kg
L = 2 m

And let length and mass of part of chain hanging down are l and m respectively
l = 0.6 m

considering mass per unit length =>

M/L = m/l

m = l / L * 4 = (0.6 / 2) * 4 = 1.2 kg 
Tension in chain hanging down = mg = 11.76 N (g=9.8 m/s^2)
Force required = Tension 
Displacement = 0.6 m (part of chain hanging comes up)
W= Force * Displacement = 11.76 * 0.6 = 7.056 J

by (2.8k points)
my teacher told me that we have to take displacement as 0.3 m, so it is wrong, right?

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