[tex]\displaystyle \frac{4}{7}(4\frac{2}{3}a-1,4)-\frac{4}{9}(6a+2,7)=\frac{4}{7}(\frac{14}{3}a-\frac{7}{5})-\frac{4}{9}(6a+\frac{27}{10})=\frac{8}{3}a-\frac{4}{5}-\frac{8}{3}a-\frac{6}{5}=-2[/tex]