Not 750 ice cream But 75cl

$$
\text{Total parts} = 3 + 4 = 7
$$

$$
\text{Dupe's share (ratio)} = 4
$$

$$
\text{Dupe's ice cream} = \frac{4}{7} \times 75 \text{ cl}
$$
$$
\text{Dupe's ice cream} = \frac{300}{7} \text{ cl} \approx 42.86 \text{ cl}
$$
Dupe will get approximately **42.86 cl** of ice cream.
$$
\text{42.86 cl}
$$