An airplane and a freight train have the same momentum. The airplane has a mass of 21,700 kg and is traveling at
1,200 km/h. The train has a mass of 9,600,000 kg.
What is the speed of the train?

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

Since the pully is a simple machine so the mechanical advantage is a 1

Newtons laws of motion