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{[(7-3)×5-2+3]÷7+9}÷a}=4

Răspuns :

{(4x5-2+3):7+9]:a=4
(21:7+9):a=4
12:a=4
a=12:4
a=3
4x5-2+3=21:7=3+9=12:3=4. a=3