Ummm x fa ayudenme con este problema ?

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<img src="https://tex.z-dn.net/?f=%20%20%5Cfrac%7Bb%28b%2B1%29%7D%7B2%7D%3D6%20%5C%5C%20b%28b%2B1%29%3D12~~--%5C%20%5Ctextgreater%20%5C%20sabemos~que~3_X4%3D12%20%5C%5C%20b%28b%2B1%29%3D3_X4~~--%5C%20%5Ctextgreater%20%5C%20igualando%20%5C%5C%20%5Cboxed%7Bb%3D3%7D%7D%20%20%5C%5C%20Ahora~calculemos~valor~de~%27%27a%27%27%2C%20veamos%3A%20%5C%5C%20%20%5Cfrac%7Ba%28a%2B1%29%7D%7B2%7D%3Db~~~--%5C%20%5Ctextgreater%20%5C%20se~sabe~que~%5Bb%3D3%5D%2C%20reemplazando%20%5C%5C%20%20%5Cfrac%7Ba%28a%2B1%29%7D%7B2%7D%3D3%20%5C%5C%20a%28a%2B1%29%3D6~~--%5C%20%5Ctextgreater%20%5C%206~es~igual~a~2_X3%20%20%5C%5C%20%5Cboxed%7Ba%3D2%7D%20%20%5C%5C%20%20%5C%5C%20Y~por~ultimo~vamos~calcular~%27%27x%27%27~veamos%3A%20%5C%5C%20%20%5C%5C%202x%2B1%3Da~~--%5C%20%5Ctextgreater%20%5C%20%5Ba%3D2%5D%2C%20reemplazando%20%5C%5C%202x%2B1%3D2%20%5C%5C%202x%3D2-1%20%5C%5C%202x%3D1%20%5C%5C%20%20%5C%5C%20%5Cboxed%7B%5Cboxed%7B%5Cboxed%7Bx%3D%20%5Cfrac%7B1%7D%7B2%7D%7D%7D%7D~~--%5C%20%5Ctextgreater%20%5C%20respuesta~alternativa~%5Ctextcircled%7Bb%7D%20%5C%5C%20%20%5C%5C%20%20%5C%5C%20." />

<img src="https://tex.z-dn.net/?f=%20%5C%5C%20%5Cmathbb%7Biiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii%7D%20%5C%5C%20%20~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Espero~te~sirva~saludos%21%21%5C%5C%20%20%5C%5C%20" />.