High$-$density lipoprotein $($HDL$)$ is sometimes referred to as the "good cholesterol". In Canada and the UK$,$ cholesterol is measured in mM $($millimolar$,$ mmol$/$L$).$ If your HDL is $250$ mg$/$dL$,$ what is this in mM$?($Hint: The molar mass of HDL is $387$ g$/$mol$.)$