we can write an equation
[tex]3.49-3.49x=3.07[/tex]where x is the change
now, solve x
[tex]\begin{gathered} 3.49-3.07=3.49x \\ \frac{0.42}{3.49}=x \\ x=0.12 \end{gathered}[/tex]and the percentage is
[tex]\begin{gathered} 0.12\times100 \\ =12 \end{gathered}[/tex]12%
