1)

[tex]7.5 + x = 4.3 \\ x = 4.3 - 7.5 \\ x = - 3.2[/tex]

2)

[tex] - 3x = 2. 1\\ x = 2.1 \div ( - 3) \\ x = - 0.7[/tex]

3)

[tex] - 3.2 + ( - 0.7) = - 3.2 - 0.7 = - 3.9[/tex]