Please help: On an athletic field, the length of one running track is exactly 400 meters. What is the distance between the front and back lines?

[Nahool77]

help needed:

On an athletic field, the length of one running track is exactly 400 meters. (Shape is half-circle ends with straight sides between.) What is the distance between the front and back lines (the straight parts) marked in red in the picture?

 

[BigBeachBanana]

help needed:

On an athletic field, the length of one running track is exactly 400 meters. (Shape is half-circle ends with straight sides between.) What is the distance between the front and back lines (the straight parts) marked in red in the picture?

Hint:
The combined-black segments is a circle, thus the distance between the red lines is the circle's diameter.

 

[The Highlander]

help needed:

On an athletic field, the length of one running track is exactly 400 meters. (Shape is half-circle ends with straight sides between.) What is the distance between the front and back lines (the straight parts) marked in red in the picture?

Further to the hint given above, you are simply tasked with finding the diameter (d) of a circle whose circumference (C) is shown below...


Please now come back and show us your working and answer, thank you.

Hope that helps.