Resposta :
Resolvendo:
[tex]Diretamente\:\:proporcionais:\\\\\frac{a}{2} =\frac{6}{12} =\frac{8}{b} \\\\Calculando:\\\\\frac{a}{2} =\frac{6}{12}\\\\12a=12\\\\a=1\\\\\\\frac{8}{b} =\frac{6}{12}\\\\b=\frac{12\:.\:8}{6} \\\\b=2\:.\:8\\\\b=16[/tex]
[tex]a+b=1+16=17[/tex]
Letra E
Espero ter ajudado!
Desculpe qualquer erro.