4× х =42 + 42 х ÷ 5 =40-20

4х = 42 + 42
4х = 84
  х = 21
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42х : 5 = 40 - 20
42х : 5 = 20
42х = 20 * 5
42х = 100
х = 2целых 16/42 = 2целых 8/21