How much time would it take for an airplane to reach its destination if it traveled at an average speed of 790 km/hr for a distance of 4,700km? what is the airplane's speed in miles/hour?

Time = (distance) / (average speed)

Time = (4,700 km) / (790 km/hr) = 5.9494 hours (rounded)

                                                   = 5hrs 56min 58 sec (rounded)

     (4,700 km) / (1.609344 km/mile) = 2,920 miles

Speed = (distance covered) / (time to cover the distance)

                       (2,929 miles) / 5.9494 hours) =  491 miles per hour

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