The given expression is
[tex]x-3y[/tex]Where x = -4/5, and y = 3/4.
Replacing the given values, we have
[tex]x-3y=-\frac{4}{5}-3\cdot\frac{3}{4}=-\frac{4}{5}-\frac{9}{4}[/tex]Now, we sum fractions
[tex]-\frac{4}{5}-\frac{9}{4}=\frac{-4\cdot4-9\cdot5}{20}=\frac{-16-45}{20}=\frac{-61}{20}[/tex]