Two points A and B are located at distances 4 cm and 5 cm respectively from a point charge $+20\mu C$. The work done in taking a charge of $+2\mu C$ from point A to point B is
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$W_{ext} = \Delta U$. Repulsion moves charges apart naturally, so potential energy decreases. $W_{ext}$ is negative, meaning energy is output, not input. Pick the magnitude match.