Thermodynamics Part 5

The internal energy of a monoatomic gas is 3 nRT . One mole of helium is kept in a cylinder having internal cross section area of 17cm2 and fitted with a light movable frictionless piston. The gas is heated slowly by suppling 126 J heat. If the temperature rises by 4∘C, then the piston will move ____ cm. (atmospheric pressure =105Pa )