Let's denote the amount of mixed fruit juice opened as \( x \) litres.

The total cost of the mixed fruit juice opened is \( 262.85x \) dollars.

The total cost of the açaí berry juice added is \( 3104.35 \times 21.333333333333332 \) dollars.

The total cost of the superfruit juice cocktail is \( 1399.45 \times (x + 21.333333333333332) \) dollars.

Since the cost of the mixed fruit juice and the açaí berry juice added together equals the cost of the superfruit juice cocktail, we can set up the following equation:

\[ 262.85x + 3104.35 \times 21.333333333333332 = 1399.45 \times (x + 21.333333333333332) \]

Let's calculate the cost of the açaí berry juice added:

\[ 3104.35 \times 21.333333333333332 = 66249.99999999999 \] (approximately \( 66250 \) dollars)

Now, let's plug this value into the equation:

\[ 262.85x + 66250 = 1399.45x + 29866.666666666664 \]

To solve for \( x \), we'll move the terms involving \( x \) to one side and the constants to the other side:

\[ 1399.45x - 262.85x = 66250 - 29866.666666666664 \]

\[ 1136.6x = 36383.333333333336 \]

Now, divide both sides by \( 1136.6 \) to solve for \( x \):

\[ x = \frac{36383.333333333336}{1136.6} \]

\[ x \approx 32 \]

So, the manager has opened approximately 32 litres of the mixed fruit juice.
개봉한 혼합 과일 주스의 양을 \( x \리터로 표시합니다.

개봉한 혼합 과일 주스의 총 비용은 262.85달러입니다.

아사이 베리 주스를 추가한 총 비용은 3104.35달러입니다.

슈퍼푸드 주스 칵테일의 총 비용은 1399.45달러입니다.

혼합 과일 주스와 아사이 베리 주스의 비용을 합치면 슈퍼푸드 주스 칵테일의 비용과 같으므로 다음 방정식을 설정할 수 있습니다:

\[ 262.85x + 3104.35 \times 21.333333333333332 = 1399.45 \times (x + 21.333333333333332) \]

아사이 베리 주스를 추가한 비용을 계산해 보겠습니다:

\[ 3104.35 \times 21.333333333333332 = 66249.9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999