please help with the following question

[a) Write down an expression for the coulomb force F between two point charges Q, and Q, that are separated by a distance r (b) Two small spheres exert an attractive force of 2.0 N on each other () How much force would they exert on each other if the distance between them is doubled? The two spheres are returned to their original separation. How much force would they exert on each other if the charge on each sphere is doubled. 14 (c) Two point charges are arranged as shown in Fig. 1.1. 10.0 em Fig 1.1 Determine the point P, where a third charge can be positioned so that it is in oquilibrium. 15]