physics Three point particles are fixed in place in an xyz coordinate system. Particle A, at the origin, has mass $m_A$. Particle B, at xyz coordinates (2.00 d, 1.00 d, 2.00 d), has mass $2.00 m_A$, and particle C, at coordinates (-1.00 d, 2.00 d, -3.00 d), has mass $3.00 m_A$. A fourth particle D, with mass $4.00 m_A$, is to be placed near the other particles. In terms of distance d, at what z-coordinate should D be placed so that the net gravitational force on A from B, C, and D is zero?