\[432 = 300 \cdot \left( 1 + \frac{8}{100} \right)^{2}\]
\[\left( 1 + \frac{p}{100} \right)^{2} = \frac{432}{300}\]
\[\left( 1 + \frac{p}{100} \right)^{2} = \frac{36}{25}\text{\ \ \ \ }\]
\[1 + \frac{p}{100} = \frac{6}{5}\]
\[\frac{1}{5} = \frac{p}{100}\]
\[p = 20.\]
\[Ответ:20\ \%.\]