Determine the equivalent inductance $L_{EQ}$ for three parallel inductor DC circuit if the values of inductance are $L_1=2mH,$ and $L_2=5mH$ and $L_3=20mH.$

Calculate the inductance of the additional inductor to be connected in parallel with the three series inductors having inductance of $L_1=2mH,$ and $L_2=5mH$ and $L_3=8mH$ if the equivalent inductance is $2\mathrm{.}5$ mH $.$