Question: Debbie Glockner-Ferrari, a whale researcher, is watching a whale approach directly toward a lighthouse as she observes from the top of this lighthouse. When she first begins watching the whale, the angle of depression to the whale is 15°50'. Just as the whale turns away from the lighthouse, the angle of depression is 35°40'. If the height of the lighthouse is 68.7m, find the distance traveled by the whale as it approached the lighthouse.