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2014-10-02T15:44:18+03:00
a+2b=15
a=15-2b  a=15-2(5+5c)=15-10-10c=5-10c
b-5c=5
b=5+5c
2a+5b+5c=2(5-10c)+5(5+5c)+5c=10-20c+25+25c+5c=35+10c