Помогите решить по действиям! 18×(11/12 - 8/9) : (5/4 + 2/7)=? 11/12, 8/9, 5/4, 2/7 - это...

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$18\cdot (\frac{11}{12}-\frac{8}{9})\div(\frac{5}{4} + \frac{2}{7})=\bf \frac{14}{43} \\ \\ 1)\frac{{11}^{(\cdot6}}{12} - \frac{{8}^{( \cdot 8}}{9}=\frac{66}{72} - \frac{64}{72} = \frac{66-64}{72} = \frac{{2}^{(\div 2}}{72} = \bf \frac{1}{36} \\ \\ 2)\frac{5^{ ( \cdot 7}}{4} + \frac{{2}^{(\cdot 4}}{7} = \frac{35}{28} + \frac{8}{28} = \frac{35+8}{28}=\bf \frac{43}{28}= 43 \div 28 = 1\frac{15}{28} \\ \\ 3)18 \cdot \frac{1}{36} = \frac{18 \cdot 1}{36} = \frac {{18}^{(\div 6}}{36}= \frac{{3}^{(\div 3}}{6} =\bf \frac{1}{2} \\ \\ 4)\frac{1}{2}\div \frac{43}{28} = \frac{1}{2} \cdot \frac{28}{43} = \frac{1 \cdot 14}{1\cdot 43} =\bf \frac{14}{43}$