A steel bolt has a modulus of 207 GPa. It holds two rigid plates together at a high temperature under conditions where the creep of the steel is described by the equation:
ε· = ε·0(σ/σo)Π
where n = 3, and ε· = 7.8 x 10-12/s, when σ = 28 MPa. The bolt is initially tightened to a stress of 69 MPa. What is the stress in it after 1 year?