This is related to couloms law.

The following figure will show the situation.

The open dot represent the q1 charge. The red dot represent the q2 and the black dot represent q3.

q1 and q2 are opposite charges. Then they will have an attraction. The atraction force is at ` ` direction `rarr` in the q1 charge.

q1 and q3 are both positive charges.Then they will repel each other. Due to this q1 will have a repel force in `rarr` direction.

The electrostatic force(F) between two charges(q1 and q2) at a distance(r) is given by;

`F = (K*q1*q2)/r^2`

`k = 8.987xx10^9Nm^2C^(-2)`

For our question;

`q1 = +8.42 muC = +8.42xx10^(-6) C`

`q2 = -5.76 muC = -5.76xx10^(-6) C`

`q3 = +5.76 muC = +5.76xx10^(-6) C`

Let;

F1 = Attraction force between q1 and q2

F2 = Repel between q1 and q3

`rarrF1 = 8.42xx10^(-6)*5.76xx10^(-6)*8.987xx10^9/(2.05)^2`

`rarrF1 = 0.1037 N`

`rarrF2 = 8.42xx10^(-6)*5.76xx10^(-6)*8.987xx10^9/(2.05)^2`

`rarrF1 = 0.1037 N`

Net force extend on q1 `= rarrF1 + rarrF2`

                                  `= 0.1037*2`

                                  `= 0.2074 N`

Net force extend on q1 is 0.2074 N.