Three charged metal spheres,

q$1=5\mathrm{.}58$ nC$,$

q$2=2\mathrm{.}96$ nC$,$

and

q$3=2\mathrm{.}56$ nC$,$

are arrayed in the xy plane so that they form an equilateral triangle with

d $=12\mathrm{.}0$ cm$,$

as shown in the figure. What is the net electrostatic force on the sphere at the origin?