Hello there here is the problem you gave us
![y=2x,x+y=9](https://img.qammunity.org/2022/formulas/mathematics/high-school/595eoyc90i526nnmnn44w7baxq2p96aipt.png)
You want to us to solve this by substitution,
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we can substitute
for
and get the equation
, do the simple algebra and we get that
, remember though
, plug in the value that
and get that
![y=6](https://img.qammunity.org/2022/formulas/mathematics/college/ffrluzwx83os6i6ndkgjpia880gpjlek6h.png)
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![{\huge{\boxed{\mathfrak{Answer}}}](https://img.qammunity.org/2022/formulas/mathematics/high-school/hbkpjroq2qnhw3c1ysi7gz31y650zhsluc.png)
Have a good day :) !