Planteamos las ecuaciones :
[1] x = 3·y
[2] 2·x + 5·y = 85
Despejamos y de [1] :
[3] y = <img src="https://tex.z-dn.net/?f=%20%5Cfrac%7Bx%7D%7B3%7D%20" />
Reemplazamos y en [2] :
2·x + 5·<img src="https://tex.z-dn.net/?f=%20%5Cfrac%7Bx%7D%7B3%7D%20" /> = 85
Sumamos las x :
<img src="https://tex.z-dn.net/?f=%20%5Cfrac%7B11x%7D%7B3%7D%20" /> = 85
Despejamos x :
x = <img src="https://tex.z-dn.net/?f=%20%5Cfrac%7B85%7D%7B11%2F3%7D%20" /> = <img src="https://tex.z-dn.net/?f=%20%5Cfrac%7B255%7D%7B11%7D%20" />
Ahora reemplazamos x en [3] :
y = <img src="https://tex.z-dn.net/?f=%20%5Cfrac%7B255%2F11%7D%7B3%7D%20" /> = <img src="https://tex.z-dn.net/?f=%20%5Cfrac%7B85%7D%7B11%7D%20" />.