find the distance bitween two given points let it be d

than apply the formula kqQ/(d*d) this will give you magnitude

and direction will be from q2 to q1

being opposite sign the force will be attractive thus force experienced by q2 will be attractive towards q1 along the st line drawn from q2-q1

on this same line choose a point to the left of q2 let the distance between q3 and q2 be x

so apply the formula

kq1q2/(d*d)=kq2q3/(x*x)

solving this you will get the required answer.............................