The percent of change is computed as follows:
[tex]\text{percent of change = }\frac{new\text{ value }-previous\text{ value}}{previous\text{ value}}\cdot100[/tex]Substituting with data:
[tex]\begin{gathered} \text{ percent of change = }\frac{8-10}{10}\cdot100 \\ \text{ percent of change =}-20\text{ \%} \end{gathered}[/tex]