What is the net force exerted by these two charges on a third charge?

Coulomb's law for the magnitude of the force F between two particles with charges Q and Q' separated by a distance d is|F|=K( |QQ'| /d^2)where K=8.854 x 10^-12 C^2/(Nxm^2) is the permittivity of free space.Consider two point charges located on the x axis: one charge, Q1 = -12.0 nC , is located at x1 = -1.705m ; the second charge, Q2 = 36.5 nC, is at the origin (x=0.0000). What is the net force exerted by these two charges on a third charge Q3 = 55.0 nC placed between Q1 and Q2 at x3 = -1.155 m?Your answer may be positive or negative, depending on the direction of the force.Force on Q3= NAnd if you could please explain how to do this problem, I would very much appreciate it! Thank You!