4. Упростите выражение 6 3/4x – x + 3 5/12x и найдите его значение при х = 1 7/11.

$$ 6 \frac{3}{4}x - x + 3 \frac{5}{12}x = 6 \frac{9}{12}x - x + 3 \frac{5}{12}x = (6 \frac{9}{12} - 1 + 3 \frac{5}{12})x = (5 \frac{9}{12} + 3 \frac{5}{12})x = 8 \frac{14}{12}x = 8 \frac{7}{6}x = 9 \frac{1}{6}x $$ $$x = 1 \frac{7}{11} = \frac{1 \cdot 11 + 7}{11} = \frac{11 + 7}{11} = \frac{18}{11}$$ $$ 9 \frac{1}{6} \cdot \frac{18}{11} = \frac{9 \cdot 6 + 1}{6} \cdot \frac{18}{11} = \frac{54 + 1}{6} \cdot \frac{18}{11} = \frac{55}{6} \cdot \frac{18}{11} = \frac{5}{1} \cdot \frac{3}{1} = 15 $$ Ответ: 15