Given:
Cost price is 420.
Profit is 30 %.
To find the selling price,
[tex]\begin{gathered} 30\text{ percent of 420 is,} \\ \frac{30}{100}\times420=126 \\ 420+126=546 \end{gathered}[/tex]Answer: the retailer must sell paper for 546 pesos to get the profit of 30 %.