The alkane shown is monochlorinated. Counting every constitutional isomer and, for each, its stereoisomers (enantiomers counted separately), how many distinct monochloro compounds are possible?

The alkane is 2-methylbutane. Four constitutional chlorides form: 1-chloro-2-methylbutane (chiral, 2), 2-chloro-2-methylbutane (1), 2-chloro-3-methylbutane (chiral, 2) and 1-chloro-3-methylbutane (1). Their stereoisomers total $2+1+2+1=6$.