I cannot solve question 9 because it refers to "worked example 1.4", which is not provided in the image. To find the net force on q1 and q2, I would need the details of the charges and their positions

I cannot solve question 9 because it refers to "worked example 1.4", which is not provided in the image. To find the net force on $q_1$ and $q_2$, I would need the details of the charges and their positions from that example.