$\lim_{x \rightarrow \infty}\frac{5^{x+1}+7^{x+1}}{5^x +7^x}$ $$\lim_{x \rightarrow \infty}\frac{5^{x+1}+7^{x+1}}{5^x +7^x}$$
I tried using L'Hospital rule,  which yielded :
$$\lim_{x \rightarrow \infty}\frac{5^{x+1} \ln 5+7^{x+1} \ln 7}{5^x \ln 5 }$$
But I'm at the dead end...  If I divide numerator and denominator by $5^x$ , I get a term $\frac{7^x}{5^x}$ ... which is unsolvable for the limit $x \rightarrow \infty $  
However , the answer provided by book is $-7$ . I doubt there is mistake in the question. 

$\dfrac{5^{x+1}+7^{x+1}}{5^{x}+7^{x}}=\dfrac{5(\frac{5}{7})^x+7}{(\frac{5}{7})^x+1}\to \dfrac{5\cdot0+7}{0+1}=7$
