Answer
$3.0 \times 10^2$ mL of ethanol.
Work Step by Step
$40.\%$ (v/v) $ ethanol $ solution : $$ 40. \space mL \space ethanol = 100 \space mL \space solution$$
$$750 \space mL \space solution \times \frac{40. \space mL \space ethanol}{100 \space mL \space solution} = 3.0 \times 10^2 \space mL \space ethanol $$
