5(3x+y)-8(x-6y)=200
20(2x-3y)-13(x-y)=520
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15x+5y-8x+48y=200
40x-60y-13x+13y=520
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7x+53y=200
27x-47y=520
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7x=200-53y |:7
x=\frac{200-53y}{7}
podstawiam do II równania
\frac{27*(200-53y)}{7}-47y=520 |*7
27(200-53y)-329y=3640
5400-1431y-329y=3640
-1760y=3640-5400
-1760y=-1760 |:(-1760)
y = 1
x=\frac{200-53*1}{7}=\frac{147}{7}
x = 21