[tex] - 7x + 9x - 11x + x = ( - 7 + 9 - 11 + 1)x = (10 - 18)x = - 8x[/tex]

[tex]12y + 3y + 20y - 9y = (12 + 3 + 20 - 9)y = (35 - 9)y = 26y[/tex]

[tex] - 5.5a - a + 5.5a + a = ( - 5.5 - 1 + 5.5 + 1)a = 0[/tex]

[tex] \frac{2}{3} a - \frac{1}{6} a + 1.2a - \frac{1}{12} a = (\frac{8}{12} - \frac{2}{12} + 1.2 - \frac{1}{12} )a = ( \frac{5}{12} + 1 \frac{1}{5} )a = ( \frac{25}{60} + 1 \frac{12}{60} )a = 1 \frac{37}{60} a[/tex]