4)

[tex] - 4(2.3x - 3) - (5 - 2.6x) + 3(0.6x - 2) = \\ - 9.2x + 12 - 5 + 2.6x + 1.8x - 6 = \\ - 4.8x + 1 = - 4.8 \times \frac{5}{12} + 1 = \\ - \frac{24 \times 5}{5 \times 12} = - 2[/tex]

5)

[tex]1.2x - ( - 0.4x + 2.4y) = 1.2x + 0.4x - 2.4y = 1.6x - 2.4y = - 0.8(3y - 2x) = - 0.8 \times - 5 = 4[/tex]