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2014-10-28T17:16:18+02:00
7a+3b=29 3a+3b+4a=29
3(a+b)+4a=29
3x7+4a=29
21+4a=29
4a=29-21
4a=8
a=8:4
a=2
a+b=7
2+b=7
b=7-2
b=5