\[- \frac{5}{6}x + \frac{4}{9}y + \frac{3}{4}x - \frac{7}{12}y =\]
\[= - \left( \frac{10}{12} - \frac{9}{12} \right)x - \left( \frac{21}{36} - \frac{16}{36} \right)y =\]
\[= - \frac{1}{12}x - \frac{5}{36}y\]