The coordinates of F' are (-9+10, -5-7) = (1, -12).
The coordinates of G' are (8+10, -5-7) = (18, -12).
The distance between F' and G' is the same as the distance between F and G, since the translation did not affect the length of the segment perpendicular to the direction of translation.
Using the distance formula:
d = √[(x2 - x1)^2 + (y2 - y1)^2]
d = √[(18 - 1)^2 + (-12 - (-5))^2]
d = √[17^2 + (-7)^2]
d = √(289 + 49)
d = √338
d ≈ 18.38
Therefore, the distance of line segment F'G' is approximately 18.38 units.