Three point charges in vacuum are place on the x-axis. Find the magnitude of force on charge 3micro C Charge.

Answer 1

Q1 at X1
Q2 at X2
Q3 at X3

k is about 9*10^9 Newton meter^2 / coulomb^2
micro Coulomb = 10^-6 Coulomb
You want the force on Q3 ?
F on 3 = + or - k Q1Q3 /(X3-X1)^2 + or - k Q2Q3 / (X3-X2)^2
pick each + or - depending on if the charges are the same sign (repels) or opposite sign (attracts)