9:
[tex]\frac{3}{4}=\frac{1}{3}+f\\\\\frac{3}{4}-\frac{1}{3} = f\\\\f = \frac{9}{12} - \frac{4}{12}\\\\f = \frac{5}{12}[/tex]
15:
[tex]y+\frac{11}{25}=-\frac{3}{25}\\\\y=-\frac{11}{25}-\frac{3}{25}\\\\y=-\frac{14}{25}[/tex]
19:
[tex]\frac{5}{6}x+\frac{1}{6}x=-9\\\\x=-9[/tex]
