Verified answer

Объяснение:

[tex]1.2(a + b) + 1.2(a + b) - a = b \\ 1.2a + 1.2b + 1.2a + 1.2b - a = b \\ 1.4a + 2.4b = b \\ 1.4a = b - 2.4b \\ 1.4a = - 1.4b \\ a = - b[/tex]