Bonjour,

a) [tex]\frac{5}{3} =\frac{5*6}{3*6} = \frac{30}{18}[/tex]

b) [tex]\frac{-12}{5} = -\frac{48}{x} = -\frac{12*4}{5*4} = -\frac{48}{20}[/tex]

c) [tex]\frac{19}{x} = \frac{-38}{-80} = \frac{-38/-2}{-80/-2} = \frac{19}{40}[/tex]

d) [tex]-\frac{x}{8,4} = \frac{1}{-14} = -\frac{14/8,4}{8,4} = -\frac{1,66666...}{8,4} = \frac{1,66666...*15}{8,4*15} = \frac{25}{126}[/tex]