Начнем с открытия скобок:

1.4 * (3 - x) - 0.8 * (x + 2) = 4.7;

1.4 * 3 - 1.4 * x - 0.8 * x - 0.8 * 2 = 4.7;

4.2 - 1.4x - 0.8x - 1.6 = 4.7;

-1.4x - 0.8x = 4.7 - 4.2 + 1.6;

-2.2x = 2.1;

x = -21/22.