It is important to be aware throughout that these questions are (deliberately!) not as 'precisely' stated as typical textbook questions. For example, the phrase 'If she had continued running ...' from lane 2 requires an assumption to be made before computation of an answer.
There is no absolutely 'right' way to make these assumptions, although assumptions need to be made clearly.
One possible assumption might be that a runner runs at their average speed for the full distance.