# Three charges $+q, 2q$ and $-4 q$ are placed on the three vertices of an equilateral triangle of each side $0.1\;m$ calculate electrostatic potential energy of the system , take $q= 10^{-7} \;c$
$\begin{array}{1 1} 9 \times 10^{-3} \;J \\ 9 \times 10^{-4} \;J \\ -9 \times 10^{-4} \;J \\ -9 \times 10^{-3} \;J \end{array}$