Two point charges 4Q, Q are separated by 1 m in air. At what point on the line joining the charges is the "electric field intensity zero? Also calculate the electrostatic potential energy of the system of charges, taking the value of charge, $Q = 2 × 10^{-7}\; C.$

$x= \large\frac{1}{3}$$m$
$U= 1.44 mj$