A compound strut consists of a steel tube of length 1 m, outer diameter 35 mm and inner diameter 25 mm which is brazed a copper tube of length 1.5 m, outer diameter 35 mm and inner diameter 20 mm. If the member carries a compressive load of 20 kN, determine the stress in each material and the overall change in length. For steel, E = 200 GN m-2, for copper E = 120 GN m-2.