Coulomb’s law for the magnitude of the force f between two

Coulomb’s law for the magnitude of the force F between two particles with charges Q and Q′ separated by a distance d is

FKQQ′d2,

where K=14πϵ0, and ϵ0=8.854×10−12C2/(N⋅m2) is the permittivity of free space.

Consider two point charges located on the x axis: one charge, q1 = -18.0nC , is located at x1 = -1.725m ; the second charge, q2 = 34.5nC , is at the origin (x=0.0000).What is the net force exerted by these two charges on a third charge q3 = 54.5nC placed between q1 and q2 at x3 = -1.120m ?