Final answer:
Without additional details or a diagram for the equilateral triangle and the positions of points D, E, F, and G, it's not possible to calculate the length of FG. In an equilateral triangle, all sides are equal, so FG could range from 0 to 13.
Step-by-step explanation:
To determine the length of the line segment FG in an equilateral triangle ABC with a side length of 13, consider that D and F are points on AC, while E and G are points on AB and BC respectively. Since the question doesn't provide information on the specific positions of D, E, F, and G, or any other relevant measurements, we cannot directly calculate the length of FG without additional details.
If FG is the entire side of the triangle BC, or a segment of it, it would range from 0 to 13 in length because BC is equal in length to AB in an equilateral triangle. Every side in an equilateral triangle is equal in length. Without more information or a diagram, we can't provide a numerical answer for the length of FG.