\(\dfrac{13}{20}+\dfrac{3}{5}+x=\dfrac{5}{6}\\ =>\dfrac{3}{5}+x=\dfrac{5}{6}-\dfrac{13}{20}\\ =>\dfrac{3}{5}+x=\dfrac{11}{60}\\ =>x=\dfrac{11}{60}-\dfrac{3}{5}\\ =>x=\dfrac{11}{60}-\dfrac{36}{60}\\ =>x=-\dfrac{25}{60}\\ =>x=-\dfrac{5}{12}\)
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\(x+\dfrac{1}{3}=\dfrac{2}{5}-\left(-\dfrac{1}{3}\right)\\ =>x+\dfrac{1}{3}=\dfrac{2}{5}+\dfrac{1}{3}\\ =>x+\dfrac{1}{3}=\dfrac{6}{15}+\dfrac{5}{15}\\ =>x+\dfrac{1}{3}=\dfrac{11}{15}\\ =>x=\dfrac{11}{15}-\dfrac{1}{3}\\ =>x=\dfrac{11}{15}-\dfrac{5}{15}\\ =>x=\dfrac{6}{15}\\ =>x=\dfrac{2}{5}\)
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\(-\dfrac{5}{8}-x=-\dfrac{3}{20}-\left(-\dfrac{1}{6}\right)\\ =>-\dfrac{5}{8}-x=-\dfrac{3}{20}+\dfrac{1}{6}\\ =>-\dfrac{5}{8}-x=\dfrac{1}{60}\\ =>x=-\dfrac{5}{8}-\dfrac{1}{60}\\ =>x=-\dfrac{77}{120}\)