Two coils are at fixed locations. When coil 1 has no current and the current in coil 2 increases at the rate $15.0 \mathrm{~A} / \mathrm{s}$, the emf in coil 1 is $25.0 \mathrm{mV}$. (a) What is their mutual inductance? (b) When coil 2 has no current and coil 1 has a current of $3.60 \mathrm{~A}$, what is the flux linkage in coil $2 ?$