Strain Energy - Problem No 1 (From previous university question papers)

A bar of 100 cm in length is subjected to an axial pull, such that maximum stress is equal to 150 MN/m^2. Its area of cross section is 2 cm^2 over a length if 95 cm and for the middle 5cm length is only 1 cm^2. If E is 200 GN/m^2, Calculate the strain energy stored in the bar.