5. (2,4a² – 7a + 6) + (0,6a² + 4a) – (a – 3)

5. $$ (2,4a^2 - 7a + 6) + (0,6a^2 + 4a) - (a - 3) = 2,4a^2 - 7a + 6 + 0,6a^2 + 4a - a + 3 = 3a^2 - 4a + 9 $$

Ответ: $$3a^2 - 4a + 9$$