A2. Cream represents $7 \%$ of the mass of milk, and from $61 \%$ of the mass of cream, butter is produced. How much milk is needed to produce $3 \mathrm{~kg}$ of butter?
(A) less than $5 \mathrm{~kg}$
(B) $17 \mathrm{~kg}$
(C) $54 \mathrm{~kg}$
(D) $69 \mathrm{~kg}$
(E) more than $70 \mathrm{~kg}$
A2. Let $x$ be the mass of milk in kg. In $x$ kg of milk, there is $0,07 x \mathrm{~kg}$ of cream. From this cream, $0,61 \cdot 0,07 x \mathrm{~kg}$ of butter is produced. It holds that $0,61 \cdot 0,07 x=3$. Therefore, $x \doteq 70,258 \mathrm{~kg}$. $3 \mathrm{~kg}$ of butter is produced from more than $70 \mathrm{~kg}$ of milk.