Median Line

The race.

Two people are going to run towards the flags. They must meet the following conditions:
They must start at the same point.
They must run the same distance
The starting point must be IN the river (not on the riverbank).

Where can they start the race?

… So, find the points of the axis of the river which are equidistant to the flags.

Bisector of an angle

You must draw an accurate clock similar to this one.