a) $$5x - 6 - (3 - 2x) = 5.7 \Rightarrow 5x - 6 - 3 + 2x = 5.7 \Rightarrow 7x - 9 = 5.7 \Rightarrow 7x = 14.7 \Rightarrow x = 2.1$$
б) $$3.4y - 4 - (9.4y + 2) = 4y - 3 \Rightarrow 3.4y - 4 - 9.4y - 2 = 4y - 3 \Rightarrow -6y - 6 = 4y - 3 \Rightarrow -10y = 3 \Rightarrow y = -0.3$$