We have the following expression:

In order to do the multiplication, we simply multiply the denominators and put the result in the denominator, and we multiply the denominators and put then in the denominator:

Before we continue, we need to determine the values of the variables for which the expression is not defined. Since we have a division, this will only happen if the denominator is equal to 0.
Since we have a multiplication in the denominator, the only way it will be 0 is if either of the factors is 0. In other words, we can't have

or

For the first equation, we simply subtract 6 from both sides and hen divide by 3 to obtain

so a cannot be -2.
For the second equation, we can actually factor is further like this:

and from this we can see that it will be 0 if a is either 4 o -4. In other words, and putting all of this together, a cannot be -2, -4 or 4.
With that out of the way, let's proceed with the multiplication:

Grouping similar terms together gives us:
