1. Lösung:
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18 + 3x = 30 - x
x = 3
Alter = 18 + 3² = 27

2. Lösung:
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18 + 3x = 30 + x
x = 6
Alter = 18 + 3*6 = 36

Allgemein gilt für Crian:
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18 +/- 3x = 30 +/- x