(b) Moving from $A\ to\ B$. $\ V_{B} - V_{A} = \left\lbrack 5 \times 10^{- 3}\left( - 10^{3} \right) + 15 + 1 \times 5 \right\rbrack$ $= 15$ volt
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Ph.D. in Physics with 19+ years of teaching experience.