electric force/field
posted by physics .
Three point charges, A = 2.2 µC, B = 7.5 µC, and C = 3.9 µC, are located at the corners of an equilateral triangle . Find the magnitude and direction of the electric field at the position of the 2.2 µC charge.
magnitude = .
N/C
direction =

You need to specify the length of the sides of the triangle, R.
Then compute the two vector forces acting on the 2.2 uC charge. The 7.5 uC charge contributes a repulsive force
F1 = k*2.2*7.5*10^12/R^2 Newtons
where k is the Coulomb constant and R is the side length in meters.
The other charge (3.9 uC) will contribute an attractive force, given by the same formula,
F2 = k*3.9*2.2*10^12/R^2 Newtons,
directed at 120 degrees to F1. Add them as vectors.