The correct answer for the exercise shown above is:
a=-4
The explanation is shown below:
1. You have the following expresssion given in the problem above:
a+6/a+4
2. By definition, the nonpermissible replacement for a is the value that make the denominator equal to zero.
3. Keeping this on mind, you have:
a+4=0
a=-4
a+6/a+4=-4+6/-4+4=2/0
Therefore, as you can see, the answer is a=-4.