Ответ:

  1. \(43x=903\), \(x=903:43=21\);
  2. \(53a=4452\), \(a=4452:53=84\);
  3. \(5243:x=49\), \(x=5243:49=107\);
  4. \(y:56=65\), \(y=65\cdot56=3640\).