The value of B when feed 3 is inverted in a material balance problem would depend on the specifics of the system, such as the flow rates, compositions, and the setup of the problem. To calculate this, you would typically need to apply material balance equations for the units involved.
However, without additional details or context, I can’t provide an exact answer for this specific question. If you have the material balance setup or more details on the problem, feel free to share, and I can help you solve it!