Solución.
Sea <img src="https://tex.z-dn.net/?f=x" /> la longitud del Río Bravo y sea <img src="https://tex.z-dn.net/?f=2x%2B332" /> la longitud del Río Amazonas, entonces :
<img src="https://tex.z-dn.net/?f=x%2B%282x%2B332%5C%2Ckm%29%3D9434%5C%2Ckm" />
Luego simplificando se obtiene :
<img src="https://tex.z-dn.net/?f=x%2B2x%3D9434%5C%2Ckm-332%5C%2Ckm%5C%5C3x%3D9102%5C%2Ckm%5C%5Cx%3D%5Cfrac%7B9102%5C%2Ckm%7D%7B3%7D%5C%5Cx%3D3034%5C%2Ckm" />
Por lo tanto :
El Río Bravo mide <img src="https://tex.z-dn.net/?f=%203034%5C%2Ckm" /> y el Río Amazonas mide <img src="https://tex.z-dn.net/?f=2x%2B332%5C%2Ckm%3D2%283034%5C%2Ckm%29%2B332%5C%2Ckm%3D6400%5C%2Ckm" />
Comprobando :
<img src="https://tex.z-dn.net/?f=x%2B2x%2B332%5C%2Ckm%3D9434%5C%2Ckm%5C%5C3034%5C%2Ckm%2B6400%5C%2Ckm%3D9434%5C%2Ckm%5C%5C9434%5C%2Ckm%3D9434%5C%2Ckm" />
Saludos.