Correct Answer - A::B
In this problem
`r_41=r_43=r_32-r_21=1m`
and `r_42=r_31=sqrt((1)^2+(1)^2) =sqrt2m`
substituting the proper values with sign in eqn ii we get
`U=(9.0xx10^9)(10^-6)(10^-6)[((4)(-3))/1+((4)(2))/sqrt2+((4)(2))/(1)+((-3)(2))/1+((-3)(1))/sqrt2+((2)(1))/1]`
`=(9.0xx10^-3)[-12+5/sqrt2]`
`=-7.62xx10^-2J`