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18+(8×a)=42, 90-(6×a)=60,(36:a)+21=30

Răspuns :

18+(8×a)=42
8×a = 42-18
8×a = 24
a = 24:8
a = 3

90-(6×a) = 60
6×a = 90-60
6×a = 30
a = 30:6
a = 5

(36:a)+21 = 30
36:a = 30-21
36:a = 9
a = 36:9
a = 4