A stepped bar ABCD consists of three parts AB, BC and CD such that AB is 300 mm long and 20 mm diameter, BC is 400 mm long and 30 mm diameter and CD is 200 mm long and 40 mm diameter. It was observed that the stepped bar undergoes a deformation of 0.42 mm, when it was subjected to a compressive load P. Find the value of P, if E = 200 GPa.

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