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:$I=RE (1−e_{−tR/2L})$
Hence
$LdI/dt=2E e_{−tR/2L}$
When $LdI/dt=E/4$
$tR/2L=ln2$
Hence $t=(L/R)(2ln2)=(L/R)ln4$