An 80-kg person hiking across a large, level plain in Zion National Park comes across a pair of large boulders. The hiker's guidebook says they have masses of 3.2 Mkg and 9 Mkg, respectively. The distance among their centers of mass is 100 meters. At what location(s) would the combined gravitational force of the two boulders on the hiker have a magnitude of 4 x 10^5 N?