Could someone answer this engineering question for me? You need to know how to do thermal stress range calculations

You have been asked to design a steel beam bridge with 6m length as a simple supported beam (e.g. Figure 1, which is located in the Blue Mountains, Australia). The beam weight is 6000N distributed over the beam length. In addition, in the worst case, two bushwalkers with 900N weight each will be on the bridge, they can pass the bridge together or individually. You only need to take the self-weight and pedestrian load into account in your calculations. Hint: you can consider two loads on the beam for each person or one load including the weight of both people. Maximum allowable stress is 100 MPa.

Question: By considering the bridge location, determine the thermal stress range. The bridge is fixed at normal temperature (18°