The inductor arrangement of Fig. $30-61,$ with $L_{1}=30.0 \mathrm{mH}$ $L_{2}=50.0 \mathrm{mH}, \quad L_{3}=20.0 \mathrm{mH},$ and
$L_{4}=15.0 \mathrm{mH},$ is to be connected to a varying current source. What is the equivalent inductance of the arrangement? (First see Problems 47 and $48 .)$