ANSWER :
25%
EXPLANATION :
The percentage increase formula is :
[tex]\frac{\text{ new - old}}{\text{ old}}\times100[/tex]The new salary is $15,000 and the old salary is $12,000
Using the formula above :
[tex]\begin{gathered} \frac{15000-12000}{12000}\times100=0.25\times100 \\ \rightarrow25\% \end{gathered}[/tex]