Final answer:
The correct loop rule formula for a given circuit involves applying Kirchhoff's loop rule, considering the direction of current flow through resistors and the orientation across sources of emf. Without the circuit diagram's specifics, one cannot definitively assign the right potential changes in the equation. The Correct answer is B. 0=+7I+8I3+21.
Step-by-step explanation:
To find the correct loop rule for the outermost loop of the circuit, we must apply Kirchhoff's loop rule, which states that the sum of the potential changes around any closed loop of a circuit must be zero.
When traversing through a resistor in the direction of current flow, we subtract the product of the current and resistance; when moving in the opposite direction, we add it.
For sources of emf (electromotive force), we add the emf value when going from the negative to the positive terminal, and subtract it when going from positive to negative.
Given the information provided, without the actual figure, we cannot determine the correct change in potentials. However, assuming standard orientation and sign convention, and knowing current directions, potential changes would be associated with current flow through resistances and emf's across batteries or other sources.
The Correct answer is B. 0=+7I+8I3+21.