EMI

Ans is b

@harshal eq resistance across inductor is
$R/2$
and at t>infinity current in circuit will be$E/R$
So current thru inductor at time t will be given by:$I=\frac{E}{R}(1e^{tR/2L})$ Hence
$LdI/dt=\frac{E}{2}e^{tR/2L}$ When
$LdI/dt=E/4$ $tR/2L=ln2$ Hence
$t=(L/R)(2ln2)=(L/R)ln4$