Solución

limx6[(x+1)f(x)]=(limx6(x+1))(limx6f(x))=28\mathop {\lim }\limits_{x \to 6} \left[ {\left( {x + 1} \right)f\left( x \right)} \right] = \left( {\mathop {\lim }\limits_{x \to 6} \left( {x + 1} \right)} \right)\left( {\mathop {\lim }\limits_{x \to 6} f\left( x \right)} \right) = 28