Answer:
1,800 ft
Explanation:
Rebecca will walk in the pattern of a regular polygon with 'n' sides and internal angles of 160 degrees (180 at a straight line - 20 degrees from each turn).
The equation that describes the internal angle of a regular polygon is:

For A = 160 degrees:

If each side is 100 ft long, the total distance that Rebecca has walked is:

She walked 1,800 ft.