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Ответ:

[tex]1) \frac{4}{a} = \frac{16}{20} \\ \frac{4}{a} = \frac{4}{5} \\ a = 5[/tex]

[tex]2) \frac{c}{8} = \frac{25}{40} \\ \frac{c}{8} = \frac{5}{8} \\ c= 5[/tex]

[tex]3) \frac{39}{27} = \frac{b}{9} \\ \frac{13}{9} = \frac{b}{9} \\ b= 13[/tex]

[tex]4) \frac{49}{32} = \frac{12}{d} \\ d = \frac{12 \times 32}{49} \\ d = \frac{384}{49} \\ d = 7 \frac{41}{49} [/tex]