A very long, straight horizontal wire carries a current such that 8.25×1018 electrons per second pass any given point going from west to east. What is the magnitude of the magnetic field this wire produces at a point 5.00 cm directly above it?

The magnitude of the magnetic field this wire produces is 5.56 × 10^-6 T

Explanation: Please see the attachments below

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current