A merchant sold goods for 39 K. How much did the goods cost, if the profit margin was the same percentage as the cost of the goods?





Translate the above text back into Hungarian, please keep the original text's line breaks and format, and output the translation result directly.
preneurial context.
A kereskedő 39 K-ért adott el árut. Mennyiért vette az árút, ha ugyanannyi százalékot nyert, mint a mennyibe az áru került?
If the merchant bought the item for $x K$, then

$$
x+\frac{x x}{100}=39
$$

or

$$
x^{2}+100 x-3900=0
$$

from which the positive root is:

$$
x=30
$$

(Viola Rezső, Budapest.)