We will write voltage drop equation as we go from A to B.\\\\({ V }_{ A }-iR+V+L\\dfrac { di }{ dt } ={ V }_{ B }\\\\)\\\\({ V }_{ A }-5\ imes 1+15-5\ imes { 10 }^{ -3 }\ imes (-{ 10 }^{ 3 })={ V }_{ B }\\\\)\\\\(V_B-V_A=15\\\\)