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a-5b=6
x=?
stiind ca:
a) x+15a-75b=300
b) 2x-24+17a-85b=690


Răspuns :

x+15(a-5b)=300
x+15·6=300
x+90=300
x=300-90
x=210

2x+24+17(a-5b)=690
2x+24+17·6=690
2x+102=690-24
2x=666-102
x=564/2
x=282