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Antwort
a = erste Zahl; b = zweite Zahl
(I) 2a - 5 = b
(II)2a + 4 = 2b
>> (I), also b, einsetzen in (II)
(II) 2a +4 = 2 (2a - 5)
2a +4 = 4a -10 |+10
2a +14 = 4a | -2a
14 = 2a |:2
7 = a >> einsetzen in (I)
(I) 2*7 -5 = b
14-5 = b
9 = b