Question

A. Calculate the net force on q2?
b. calculate the net force on q3?

q1= +2.0 MC
q2=+3.0 MC
q3=+6.0 MC

q1-----30cm-----q2-----------45cm----------q3

Answer 1

see Coulomb's law.

Answer 2

Use superposition. First find the effect 1 has on 2. Then find the effect 3 has on 2. Then addthem together paying close attention to direction.
Same for part b