2. The Boltzmann superposition principle implies that we can describe the stress relaxation (or creep) of a material by summing up all of the strains (or stresses) that we apply to a material. In the case of stress relaxation, it states that: (t)=iG(tti)di where G(t) is the time-dependent modulus given by the Maxwell model, and di is a step strain applied at time ti. A particular polymer is well-described by the Maxwell model, with a viscosity M=600MPas and an elastic modulus of GM=20MPa. The material is exposed to a series of step strains: At t=0s, a step strain of d0=0.005 is applied. 20 seconds later, a second step strain of d1=0.1 is applied. Finally, after a total elapsed time of t=60s, a third step strain of d2=0.01 is applied. What is the stress in the material at t=120s