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Solve the following systems by substitution: x – 4y = 9
2x – 3y = 11

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Mlcparra16id
We make the first equation as follows:
x - 4y = 9
x = 9 + 4y 

So:
2x - 3y = 11
2(9 + 4y) - 3y = 11
18 + 8y - 3y = 11
5y = -7
y = -7/5

So:
x = 9 + 4y 
x = 9 + -28/5 = 17/5