The correct answer for the exercise shown above is:
zero (0)
The explanation is shown below:
1. You have the following expression given in the problem above:
7/6a
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:
7/6a=7/6(0)=7/0
Therefore, as you can see, the answer is: zero (a=0).