How to calculate $$\lim \_{x\to \infty}\left(\frac{3x^2+7}{2x^2+4x}\right)^{3x}$$

I see that the sequence grows without a bound so I think that 

$$\lim \_{x\to \infty}\left(\frac{3x^2+7}{2x^2+4x}\right)^{3x}=\infty$$

but how can I prove it in the right way