Solución
$$\mathop {\lim }\limits_{x \to 6} \left[ {f\left( x \right) + {1 \over 3}g\left( x \right)} \right] = \mathop {\lim }\limits_{x \to 6} f\left( x \right) + {1 \over 3}\mathop {\lim }\limits_{x \to 6} g\left( x \right) = 7$$