3 charged particles are placed at the corners of an equilateral triangle of side d = 1.15 m. Q1 = +4.0 µC Q2= -6.0 µC Q3 = -6.0 µC....

The charge on Q1 by Q2 and Q3 are (1/4pie0)*Q1Q2/d^2 and
(4pie0)^(-1)*Q1Q3/d^2 =
0.163327N

9*10^9*4*6*10^(-12)/1.15^2 =
 0.163327N attraction as the charges are different,
and

9*10^9*4*6*(10^(-12)/1.15^2 = 0.163327N attraction as
the charges are different.

Therefore the net force is of
the two equal magnitude force with 60 deg between  by law of parallelogram is
 (0.163327)2cos30 = 0.282890717 N  with 270 degree to X
axis.

In a similar way we can show that the force on Q2 is
0.282990717N acting 30 degree to X axis.

In a similar way
we can show that the force on Q3 is 0.282990717N acting 150 degree to X
axis.