Two point charges +9 µC and +1 µC are placed 10 cm apart in air. Find the distance from the +1 µC charge along the line joining them where the net electric field is zero (other than at infinity).
a) 7.5 cm between the two charges
b) 1.0 cm between the two charges
c) 2.5 cm between the two charges
d) 5.0 cm on the side away from the +9μC charge