Johnny is currently struggling with math problems that require him to "carry" the tens place to the next column. even with an expert instructor, johnny is not ready to learn algebra. learning algebra would be in the limit of the zone of proximal development for johnny.

I believe the answer is: Outer
In this context, outer limit of the zone of proximal development refers to the type of accomplishment that we couldn't achieve without the help of other individuals. In the scenario above, learning algebra is the form of accomplishment and the expert instructor is the individuals who had to help him if he want to succeed.