Пошаговое объяснение:

[tex]1) - 2.4a \times ( - 5b) = 2.4a \times 5b = \frac{12}{5} \times 5 ab= 12ab[/tex]

[tex]2)9a - a - 8b + 3b = 8a - 5b[/tex]

[tex]3)a + (a - 10) - (15 + a) = a + a - 10 - 15 - a = a - 25[/tex]

[tex]4) - 4(b - 4) + 7(b + 2) = - 4b + 16 + 7b + 14 = 3b + 30 = 3(b + 10)[/tex]