Two point charges of magnitudes +q and +4q are fixed 45 cm apart in air, the smaller charge being at point X.
a. (i) Calculate the distance(s) from X along the line joining the charges at which a small positive test charge would experience zero net electrostatic force.
b. (ii) If the test charge is displaced slightly towards the smaller charge from the null point lying between the two charges, state the initial direction of the net force acting on it.