the core$-$and$-$coil inductor in example $2\mathrm{.}10$ of masters had an inductance that varied from$18\mathrm{.}8$ mH to $31\mathrm{.}3$ mH when the material's relative permeability ranged from $15,000$ to $25000.$ find the range of inductance that would result if the core is built with a $0\mathrm{.}001$m air gap