2(x+3) - 3(x+1) = 9

2*(x+3) - 3*(x+1) = 9

2x + 6 - 3x - 3 = 9

-x +3 = 9           =>         -x = 6         =>   x = 6

Test:     $${\mathtt{2}}{\mathtt{\,\times\,}}\left({\mathtt{\,-\,}}{\mathtt{6}}{\mathtt{\,\small\textbf+\,}}{\mathtt{3}}\right){\mathtt{\,-\,}}{\mathtt{3}}{\mathtt{\,\times\,}}\left({\mathtt{\,-\,}}{\mathtt{6}}{\mathtt{\,\small\textbf+\,}}{\mathtt{1}}\right) = {\mathtt{9}}$$

Gruß radix !