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2014-02-12T00:22:39+02:00
A+b+c+d=67
a-x=9
b-x=15
c-x=11
d-x=12
x+9+x+15+11+12+x+x=67
4x=20
x=20:4=5
a=9+5=14
b=15+5=20
c=11+5=16
d=12+5+17
1 5 1