Numerical answer type, tolerance 0.5.
Answer: 3
The alkene shown is 3-methylbut-1-ene. Protonation gives the secondary 3-methylbutan-2-yl cation, which is trapped as 2-bromo-3-methylbutane (one stereocentre, so 2 enantiomers). A 1,2-hydride shift gives the tertiary 2-methylbutan-2-yl cation, trapped as 2-bromo-2-methylbutane (achiral, 1 compound). Stereoisomer enumeration with RDKit confirms 2 + 1 = 3.