24.11. a) 2x ⋅ 4y - 3x ⋅ 2y - 0,2x ⋅ 5y + y ⋅ 5x - 5xy + 8xy;

Приведем подобные члены:

$$2x \cdot 4y - 3x \cdot 2y - 0{,}2x \cdot 5y + y \cdot 5x - 5xy + 8xy = 8xy - 6xy - xy + 5xy - 5xy + 8xy = (8xy - 6xy - xy + 5xy - 5xy + 8xy) = 9xy$$

Ответ: $$9xy$$