Помогите решить уравнения

А)
$0.15(x - 4) = 9.9 - 0.3(x - 1) \\ 0.15x - 0.6 = 9.9 - 0.3x + 0.3 \\ 0.15x - 0.6 = - 0.3x + 10.2 \\ 0.15x + 0.3x = 10.2 + 0.6 \\ 0.45x = 10.8 \\ x = 10.8 \div 0.45 = \frac{108}{10} \div \frac{45}{100} = \frac{108}{10} \times \frac{100}{45} = \frac{12 \times 10}{5} = 12 \times 2 = 24$
Ответ: 24.

б)
$1.6(a - 4) - 0.6 = 3(0.4a - 7) \\ 1.6a - 6.4 - 0.6 = 1.2a - 21 \\ 1.6a - 7 = 1.2a - 21 \\ 1.6a - 1.2a = - 21 + 7 \\ 0.4a = - 14 \\ a = - 14 \div 0.4 = - 14 \div \frac{4}{10} = - 14 \times \frac{10}{4} = - \frac{140}{4} = - 35$
Ответ: -35