A tiny sphere with a charge of q = +8.0 µC is attached to a spring….

A tiny sphere with a charge of q = +8.0 µC is attached to a
spring. Two other tiny charged spheres, each with a charge of
❝4.0-µC, are placed in the positions shown in the figure, in which
b = 4.5 cm. The spring stretches 5.0 cm from its previous
equilibrium position toward the two spheres. Calculate the spring
constant.