b: \(\dfrac{-x}{3}=2\dfrac{1}{7}:\dfrac{5}{7}\)
=>\(\dfrac{x}{-3}=\dfrac{15}{7}:\dfrac{5}{7}=\dfrac{15}{7}\cdot\dfrac{7}{5}=3\)
=>\(x=-3\cdot3=-9\)
c: \(\left(3,5-2x\right)\cdot1\dfrac{1}{3}=-20\%\)
=>\(\left(3,5-2x\right)\cdot\dfrac{4}{3}=-\dfrac{1}{5}\)
=>\(3,5-2x=-\dfrac{1}{5}:\dfrac{4}{3}=-\dfrac{1}{5}\cdot\dfrac{3}{4}=-\dfrac{3}{20}=-0,15\)
=>2x=3,5+0,15=3,65
=>\(x=\dfrac{3.65}{2}=1,825\)
d: \(\dfrac{5^x}{125}=5\)
=>\(5^x=5\cdot125=625\)
=>\(5^x=5^4\)
=>x=4