I did not find this intuitive, nor high school level. I bow to your high school. I admit I find it difficult to apply the right hand rule trying to figure out the positive and negative field calculations to the flow of B-field calculations. Since the currents are flowing in opposite directions the B-fields act against each other and are therefore additive. However, assuming a 2-D representation, and assuming a plane through the center of the wires parallel to the direction of the current flow.