Ответ:

  1. \(\frac{x}{5}=8\)
    \(x=8\cdot5=40\)
  2. \(\frac{y}{7}=9\)
    \(y=9\cdot7=63\)
  3. \(\frac{3x}{4}=12\)
    \(3x=48\)
    \(x=16\)
  4. \(\frac{5y}{6}=15\)
    \(5y=90\)
    \(y=18\)

Ответ: x = 40; y = 63; x = 16; y = 18.