The a is Right Where it Should Be

Calculus Level 3

$\displaystyle \sum_{x=1}^{\infty} \left [ \ln\left(\dfrac{x+4}{x}\right)-\ln\left(\dfrac{x+6}{x+2}\right) \right ] =\ln(a)$

Evaluate the following sum above and solve for the value of $a$ .

Try the harder version here