If the armature current in a $240-$volt d$-$c motor with a $0\mathrm{.}05-$ohm armature resistance should be limited to $300$ amp, how much resistance should the starter insert in series with the armature at a point where the cemf is $225$ volts?

A$.0\mathrm{.}00$ ohm

B$.0\mathrm{.}75$ ohm

C$.975$ ohms

D$.0\mathrm{.}05$ ohm