Three point charges, each with charge \(+q\), are initially fixed at the vertices of an equilateral triangle with side length \(d\). The net electrostatic force on any one of the charges has magnitude \(F_i\). The charge at one vertex is then replaced by a charge of \(-q\), while the remaining two charges remain \(+q\). What is the ratio \(F_f / F_i\) of the new net electrostatic force magnitude \(F_f\) on one of the remaining \(+q\) charges to its initial magnitude \(F_i\), and what is the direction of this new net force?