I want to understand this concept more than anything so advice as well as hints to solve this problem are greatly appreciated.

Question

26. Two fixed charges, -4.0E-6 C and -5.0E-6 C, are separated by a certain distance.

a) is the net electric field at a location halfway between the two charges
1) directed toward the -4.0E-6 C charge
2) zero
3) directed toward the -5.0E-6 charge.

30)Two charges of +4.0 E-6 C and +9.0 E-6 C are 30 cm apart. Where on the line joining the charges is the electric field zero?

Answer 1

a. E is the direction a + charge goes, so it will be directed to the -5E-6charge

30)

k4E-6/x=k9E-6/(.3-x)

solve for x, the distance in meters from the smaller charge.