Multiply the top and bottom number of the second fraction by 2, so both fractions have the same denominator (bottom number)
[tex]-\frac{5}{6}-\frac{2}{3}\times\frac{2}{2}[/tex][tex]-\frac{5}{6}-\frac{4}{6}[/tex]Subtract the numerators (top numbers) and keep the same denominator
[tex]-\frac{9}{6}[/tex]