AYUDA , método sustitución?

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<img src="https://tex.z-dn.net/?f=%5Cmathrm%7BDespejar%7D%5C%3Ax%5C%3A%5Cmathrm%7Bpara%7D%5C%3A%281%29%3A" />

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<img src="https://tex.z-dn.net/?f=%5Cfrac%7B39y%2B20%7D%7B15%7D-%5Cfrac%7B1%7D%7B3%7D%3D-%5Cfrac%7B2%7D%7B5%7Dy" />

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