well, yesterday was 2.90 and today is 2.84, it dropped 6 pennies or $0.06.
now, if we take 2.90 to be the 100%, how much is 0.06 off of it in percentage?
[tex]\bf \begin{array}{ccll}
amount&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
2.90&100\\
0.06&p
\end{array}\implies \cfrac{2.90}{0.06}=\cfrac{100}{p}\implies p=\cfrac{0.06\cdot 100}{2.90}[/tex]