The addition of HBr is according to Markownikoff s rule in this reaction. $ C{{H}_{3}}-\underset{\begin{smallmatrix} | \\ C{{H}_{3}} \end{smallmatrix}}{\mathop{CH}}\,-CH=C{{H}_{2}}+\overset{+\,\,\,-}{\mathop{HBr}}\,\xrightarrow{{}} $ $ C{{H}_{3}}-\underset{\begin{smallmatrix} | \\ C{{H}_{3}} \end{smallmatrix}}{\mathop{CH}}\,-\underset{\begin{smallmatrix} | \\ Br \end{smallmatrix}}{\mathop{CH}}\,-C{{H}_{3}} $