Bonsoir,
[tex] \dfrac{\dfrac{-1}{3}}{5} =\dfrac{4}{x} \\\dfrac{-1}{3}*\dfrac{1}{5} =\dfrac{4}{x} \\\dfrac{-1}{15} =\dfrac{4}{x} \\-1*x=4*15\\-x=60x=-60 [/tex]