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Решите задачу:

$5ax = 14 - x \\ 5a \times 4 = 14 - 4 \\ 20a = 10 \\ a = 10 \div 20 \\ a = 0.5$

$5x - 0.4(7x - 9) = 2.94 \\ 5x - 2.8x + 3.6 = 2.94 \\ 2.2x = 2.94 - 3.6 \\ 2.2x = - 0.66 \\ x = ( - 0.66) \div 2.2 \\ x = - 0.3$

$- 3(2.1x - 4) - 1.9 = 1.2(0.5 - 5x) + 2.6 \\ - 6.3x + 12 - 1.9 = 0.6 - 6x + 2.6 \\ - 6.3 + 6x = 3.2 - 12 + 1.9 \\ - 0.3x = - 6.9 \\ x = - 0.69 \div ( - 0.3) \\ x = 23$