well, from 340 down to 150, their difference is 190.
now, if we take 340 to be the 100%, what is 190 off of it in percentage?
[tex] \bf \begin{array}{ccll}
amount&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
340&100\\
190&p
\end{array}\implies \cfrac{340}{190}=\cfrac{100}{p}\implies p=\cfrac{190\cdot 100}{340}\implies p\approx 55.88 [/tex]
